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Vorshlag C4 Corvette TT Build: Project DANGER ZONE

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  • #16
    Re: Vorshlag Budget TT Build: Project DANGER ZONE

    continued from above

    The targa top was modified to fit around the cage. The metallic structure of the 22.6 pound assembly was removed, leaving just the outer skin. This wasn't ideal but necessary. The skinned plexiglass panel has the right curvature and was mocked up to make sure the windshield frame and B-pillar structure still fit.

    The roof panel mounts shown above were fabricated (and logged under the cage work) and welded to the top of the factory windshield surround and the top of the B-pillar roof structure. On top of each is a poly bushing, machined to the correct angle, bonded to the steel mount, and with a thru-hole for the mounting bolts. Mounting the plexiglass to the cage at only one end could allow the flimsy plexiglass to buckle under load, so the "flexible" OEM roof structure that was left was used instead.

    This plexiglass top mounts with flush mounted stainless bolts in 5 places and keeps the airflow going where it should, but that's about it. The top is still somewhat translucent, which isn't ideal, but it wasn't worth the time to fabricate this complex curved roof panel out of aluminum or even skinning the plexi in vinyl film. Yet.

    While adding the cage, it made sense to add the nets and other safety gear required for wheel to wheel racing; this car could be run in PTC (W2W) as well as TTC (Time Trial). A Schroth center net was added first, and it passes through the dashboard surround that we added. As I showed in my first post, this car came to us with just the gauges attached to the fiberglass inner dash structure, but I wanted more of the original dash pad and gauge binnacle installed. It looks more complete and professional, plus provides better anti-glare protection. Ryan managed to save what he could from the old dash pad that came with the C4, clearanced that and the inner structure to clear the roll cage dash bar, and mounted the gauge cluster back in the original binnacle.

    Left: Before, with no dash pad or gauge "binnacle". Right: OEM binnacle added as well as about half the dash pad

    A metal panel was added for a section and a toggle switch for the OEM traction control defeat was added. This really needs a momentary on/off push button but this works for now (it simply grounds a circuit) to disable the ASR. The driver's door net was a bit more complicated, as they always are. Ryan made a lower frame that has a slide-thru mount that can slip down and out of the way when unlatched, but gets rigid when the net is latched in place. The upper frame pivots at the back on a spherical, to allow it to swing down and in/out a bit.

    We added padding at the last minute, as the car was being loaded onto the open 2 car trailer - in the rain. I had hoped we would have time to paint the cage/interior at Heritage but we started about a week too late, as our shop schedule was just too overloaded. So we got to this point for safety...

    Suspension Upgrade

    After the cage work was completed by Ryan, Olof tackled the oil leaks next, starting about 3 days before the race weekend. In my last update I asked folks what they thought we should spend the remaining 3 points in TTC on: springs, shocks, exhaust, etc. We took this input and looked at the (somewhat limited number of) lap data from MSR-H and went ahead and decided: SPRING UPGRADE would be worth 2 of those 3 points.

    This base trim model 1992 C4 has the original FE1/FX3 springs (417 #/in front, 227 #/in rear - with wheel rates that are lower than that) with longer lowering bolts out back. Matteucci had already added the aftermarket shims/tricks to lower the front. It still sits very high up front, too. I was hoping to stick with Hyperco C4 springs at both ends, since we are a dealer, but their mold to make the C4 front spring was damaged last year and it would cost $70K to replace it. So yea, Hyperco is out of the C4 front spring business. I next called Paul at Vansteel and had a good conversation with him. He had better Hyperco data on the C4 than Hyperco, and recommended the Vette Brakes Products (VBP) "Xtreme" front spring, shown below.

    This VBP front spring is different from the OEM C4 style front springs, in that it is flat and has adjustable ends like a C5 front spring. He told me of a number of racers using this successfully and it was the one he used on most C4's like ours (track use). McCall also had good luck with this spring on his 1989 Corvette LT4 he runs in BSP class autocrossing. I've driven that car and it WORKS.

    The C4 rear spring mounts with adjustable bolts at the ends, so you can alter ride height stock. Here are the OEM 1992 + 1984 rear springs

    So then I called VBP and the guys there helped me narrow in on a spring rate for their front spring - which can be built from 1000-1250 pounds/inch. We decided on 1200 and they custom built a spring for us that measured out at 1170 pounds/in.

    For the rear I had picked up a 1984 Z51 rear spring from Matteucci with the car purchase, and it turns out to be the stiffest OEM spring ever offered on the C4 at 500-510 #/in. That end is easily ride height adjustable with these lowering bolts, which come in various lengths for extreme lowering. We stuck with the ones that Matteucci had and got to the ride height shown below. This is about 3" lower than stock up front and 2.5" out back, which lowers the CG significantly but doesn't get the rear suspension into any funky geometry (going lower can).

    In case you were looking at the math, we increased the front spring rate by 2.8 times (417 to 1170 #/in) and the rear by 2.25 times (227 to 510 #/in), which is fairly typical of where we start for most IRS cars. Sometimes we don't go quite as far in the rear as we did here, but our spring choices were limited and I really like a car that "rotates well". I was not disappointed with the handling on track, either.

    Oil Leak Fixes!

    So our debut with NASA @ MSR-H had very limited laps due to massive smoke from leaks at the Rear Main Seal (RMS) and oil pan gaskets. We were limited to 1-2 lap blasts before the smallish oil leaks started to get on the exhaust and caused smoke. The oil drops stayed off the track - until you stopped, then it would miss the exhaust and drip straight down.

    Matteucci warned me before I bought the car that he thought both the RMS and oil pan gaskets needed to be fixed. He did the clutch job and Moroso oil pan install on jack stands, and it is nearly impossible to do those two things correctly on a C4 without a lift. The big Moroso oil pan has kick-outs for extra oil capacity and trap doors for better oil control while cornering - strongly recommended for LT1 motors on a road course.

    To get to the RMS the transmission has to come out, and that's no small task. Olof spent about 2 days doing this repair + the spring swap above, and it was finished at the last minute - we didn't load up and leave for MSR-C until 5:30 pm Friday (had planned on leaving by 12 noon to get a good spot).

    The C-channel/torque beam, driveshaft, shifter then trans were removed. Next the complicated QuarterMaster triple disc 7.25" diameter clutch pack and flywheel was removed, then the 3 pound starter flex plate. The weights are shown below.

    This is how you remove over 50 pounds from your flywheel/clutch mass. And this is what makes the motor rev!

    We replaced the locking nuts on the clutch pack but put the sintered bronze plates back in, as the wear looked great. We had thought about swapping to their twin disc Kevlar "rally clutch" set-up, which uses the same cage and flywheel. This set-up is supposed to be more forgiving on slow speed driving (paddock, between rally stages) but I have gotten used to the triple disc and we decided to stick it back in since it looked good.

    The oil pan had some NASTY funk in it, which made us all VERY concerned. We found a hole in the intake boot that might have let some dirt past the air filter, but more than likely this is just normal wear. The grit was very fine, grey in color, and magnetic/ferrous, so probably indicative of worn piston rings. Well it made great power a month ago on the dyno, how bad could it be? We didn't have time to do a compression or leak down test, so I had Olof clean out the pan and slip in a fresh FelPro gasket and get it buttoned up. With the car on the lift and two removable subframe members removed it was easier to install it straight and true.

    We used the $300 LT1-specific RMS installation tool and got the new $10 seal installed square to the crank as well. Both the RMS and oil pan gasket had small rips in them, allowing the oil leak to happen. The exhaust went back on, fresh 15W50 Mobil1 oil and filter went in, and it fired right up. Runs much better with the hole in the intake boot and TPS sensor fixed, it seems.

    Yep, the Throttle Position Sensor (TPS) and intake boot were both replaced. The TPS repair removed the dead spot I noticed at about 2200 rpm/light throttle, so that was money well spent. The factory intake boot is unique to the 1992 model year, and is no longer made. The closest thing we could find was the $50 silicone boot from Mid-America Corvettes, which isn't exactly like the (now out of production) stock piece, so we have to (temporarily) take a 1 point hit for Cold Air Modifications. We may or may not revisit that point later.

    I updated the classing sheets for both the Corvette and the Mustang while the guys weighed the C4. We picked up about 45 pounds in the front cage structure (1.75" x .095" wall DOM) so they pulled one 45 pound plate out of the ballast box and away we went. We kept the same brakes, tires and other bits on the car from the previous race in January. No time to swap the rear hatch to plexiglass or anything else - go go go!

    Time & Parts Budget To Date

    I've been promising to show the hours and parts costs from the beginning but I write these posts when I have time and I have been very busy lately, trying to run the business and make CNC machined parts (feed the machines!). I finally stopped long enough to add up some costs. Let's look at hours first...

    Hours Spent To Date = 104.94 hours, logged per MyShopAssist

    I was guessing close to 100 hours and that was pretty dang close. We log all jobs, both customer work and our internal test mules and race cars. The only work not counted was my hours for installing the front brakes and cleaning the front suspension (about 4) and Jon's hours cutting and installing the decals (about 3). Here's the breakdown:

    Round 1 - work before MSR-H
    • Mounting and balancing the R7 tires on the Enkei wheels = 1.02 hours
    • Install OEM replacement Bilstein shocks = 1.35 hours
    • First Oil + Filter Change (8 qts Mobile1 15W50) = .45 hours
    • Caliper + bracket + pin replacement for correct unit = .68 hours
    • 4-point Roll bar fab + cover plates + fire bottle install + floor pan repair + hatch removal/install = 51.23 hours
    • Sub-total before first race = 54.73 hours

    Round 2 - work before MSR-C
    • Roll cage completion (front half + roof structure removal/install) = 29.23 hours
    • Ballast mount fabrication + machining = 5.32 hours
    • Oil pan gasket + RMS repair (+ driveshaft, torque arm, trans and clutch R&R and 2nd oil + filter change) = 11.19 hours
    • Front and rear spring installation (including fixing the VBP spring mounts) = 3.97 hours
    • Sub-total before first race = 49.71 hours

    As for costs, its still around $5000 total, all-in. I will do a better budgetary break down next time, when I have more time to make the "report" in our accounting software. We lost our Operations Manager and it took me 3 weeks to look for and hire a replacement, who starts on Monday. It has been crazy busy around here and we've been down a man for 2 weeks, ugh.

    This Week At Vorshlag - March 12, 2015

    The video below shows a good bit of the work Olof tackled with the clutch, springs, and gasket/seal repairs. Its 7 minutes long and also touches on some other fabrication work + some of the CNC work Jason and I have been buried with for weeks.

    YouTube video:
    SmugMug video: LINK

    I've finally set-up our new Vorshlag YouTube channel and will start to post various videos there, as they seem to work better than our SmugMug video hosting (which seems to wreck the videos on mobile devices).

    That's all I have for this time.

    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


    • #17
      Re: Vorshlag Budget TT Build: Project DANGER ZONE

      Project Update for April 23, 2015: Well the second NASA event in Project #Dangerzone did not go according to plan, but I had a bad feeling about the motor when Olof had the oil pan off and stuck a flash light up into the cylinders. I will cover the March Motorsports Ranch - Cresson event in the C4 below.

      We also brought our TT3 prepped Mustang, so if you have read that car's latest build thread update, this NASA @ MSR-C "race report" section is verbatim from the massive four-part April 23rd update there. There is additional information below that race report about what's coming next on DangerZone...

      March 14-15 - NASA @ MSR-Cresson. Running the '92 Corvette in TTC + '11 Mustang in TT3

      Since we brought and I drove 2 cars for this weekend, this portion below will be shared in both the TT3 Mustang thread and the TTC Corvette thread.

      Vorshlag Event Photo Gallery:

      We were pretty far behind on prepping the Corvette, and we saw some issues inside the motor with the oil pan off that worried me a great deal. Luckily I had signed our team entry "Team Vorshlag" up for a double entry with two cars (paid twice). This meant that Amy and I could both drive both cars in TT that weekend. So in case she wasn't winning in TT3, I could hop in the Mustang for a session and give it a go. Or if the Corvette had problems, which I suspected it just might, I could still get some seat time in the Mustang.

      We didn't quite get the C4 prepped by the deadline I had hoped for, but our techs only work on Vorshlag owned cars when we have time between customer cars. Since we were slammed we had to squeeze in some time, but it was neither long enough nor soon enough. Since there was no time to track test the C4 after this big round of changes, this event would be the first time running this car with a brand new cage/nets, new spring set-up/ride heights, and then some items were unfinished. There were also some potential problems uncovered when we replaced the leaking rear main seal and oil pan gaskets.

      You can see a lot of the C4 prep in this "This Week At Vorshlag" video from March 12, 2015

      Scoring in the bottom of some cylinders was evident. A thick coating of metallic grit was in the bottom of the oil pan, which was magnetic so that meant it was ferrous. Likely this meant we had smoked a piston ring or two (or eight). But when the oil pan and trans were buttoned up, the car ran fine and had no smoke. More importantly, ALL of the oil leaks were gone.

      The cage work was rushed and we ended up installing the SFI padding while loading the car onto Mike M's trailer at 5:30 pm, then loaded the TT3 Mustang into our trailer, and left the shop at 6 pm - about 6 hours later than I had hoped. It had been spitting rain all day but the predictions were clear for Sat-Sunday. We knew that this weekend was going to be crowded and both Mike and we were trying to get good paddock spots. Turns out it was a record attendance for ANY event at MSR-C with 220+ entries, many of whom got there early Friday to test, so we were parked in the grass when we arrived Friday evening. This made loading/unloading more difficult and we had to watch the splitter for scrapage on the paddock road, plus hot Hoosiers always got covered in dead grass when we came in off track.

      We got Mike's 2012 Mustang and the Corvette unloaded off his open 2 car trailer, then our Mustang unloaded from our trailer right before dark. We then reloaded the Corvette (no side windows) into our enclosed trailer, since it looked like rain might hit over night. Amy, me and Mike unhooked the two trailers and we went to dinner in Granbury at the 1890, best restaurant in town. Amy and I stayed in Granbury at the Hilton Garden Inn, 15 miles from the track but it is worth the drive - not to mention the one hotel in Cresson fills up months in advance for race weekends.

      I'm glad we brought both cars. We got to the track early, then scrambled to get both cars ready without any crew to help (mistake). TT meeting was brief, check tire pressures and fuel levels, then I suited up and climbed into the C4 while Amy got ready in the Mustang. I went to grid and started mid-pack for the "Saturday Practice" session, which doesn't count for TT competition but the times are used to establish grid position. Scrubbed in the used R7 tires from the January event and they felt great. I got into a group with the front cars that quickly pulled away on the first hot lap, with nobody behind as far as I could see.

      The C4 felt FAST and the handling was much improved with the new spring rate set-up, but there was a LOT OF SMOKE coming out of the exhaust. I knew it wasn't the RMS or oil pan, and it wasn't leaking oil, but definitely out of the exhaust and only when under power. I took 3/4 of this hot lap at speed and no oil was getting onto the tires so it felt fine, but I knew I'd get a black flag. I feared there was something seriously wrong inside the motor - broken piston ring or ring land? - and excessive blow-by was pumping out through the PCV system, into the intake, burning it in the combustion chamber, then sending it out the exhaust.

      I was driving my own line but watching the mirror for the exhaust smoke and watching the corner workers for black flags, thinking "Not AGAIN!", I lifted for the last 2 corners and coasted into the pit entrance way off the pace. This was somehow still a 1:25 lap, beating the old track record by 2 seconds. Coasting. GRR!

      Video of the C4's first "throw-away" lap - which was the fastest it ran all weekend, and 2 sec ahead of the TTC record?!

      After the Warm-up session my half-aborted 1:25.097 lap was was 9th fastest overall in TT and I was somehow in the lead over 5 other TTC cars in class, but the next closest car was only 1/2 second back. I knew this was going to be short lived and the time wouldn't stand because it was during the "practice" session.

      I figured we could fix the issue and make it back out later that day. After getting fuel (filled up after every session to maintain weight - even through it never got weighed), I came back to paddock and climbed out of the car (wearing the HANs was torturing my back on the way out of the cage each time). Amy pulled up, also in from the session early? She said the engine was cutting out BADLY, just like at COTA.

      So great.... now I had two broken cars to fix, when traditionally we have had near perfect performance week after week in the past 4 years. I started to think and remembered two years ago when the Mustang ran poorly at ECR in 2013 - it was a bad Wide Band O2 sensor. The front two O2 sensors are Wide Band and help the engine tune itself as it runs. The after-catalyst O2s just make sure the cats are working and don't do anything to the performance or tune.

      We had replaced both of these wide band O2 sensors before, but it had been 2+ years. So we changed out of racing suit and gear, started up the F350 and ran into Ft. Worth looking for parts. We rounded up a new Wide Band O2 at Ford Dealer (after trying 3 parts places), paying too much but happy to find it. Then stopped at Wal-Mart to get more Mobil1 for the C4, then at a NAPA on the way to get parts to try to make a remote breather/catch can for it as well.

      By the time we had gotten back TT session 1 was underway, but we had work to do. Parked in the grass we drove the Mustang up on the Race Ramps and I changed the O2 sensor, which was a back breaker, but it fixed the issue completely and it has run fine ever since. Initially I had hoped the C4 smoke was maybe a weird stuck PCV issue, so we pulled it out of the system and plumbed the crankcase to a big external breather. Sure enough, short test drives on city streets showed it was smoke free. After lunch on Saturday we took both cars out again, and Amy was fine but the C4 smoke was back, and worse than ever.

      Amy was flying away from me as I took a single lap in the C4, immediately smoking. I came through Ricochet sideways at 100 mph, with a tiny bit of oil dripping out of the breather and getting onto the right rear tire. Doesn't take much! I immediately slowed down and pulled off line, waving drivers by. The smoke stopped but I was still getting waving black flags, telling me to come in for a "look". Pretty scary, horrible lap coasting and getting out of everyone's way. Called it quits for the weekend for the Corvette, as there was no fixing it track-side (needs engine internals).

      My temporary "breather mod" only made matters worse, so I shut it down after less than a 1/2 lap. "....MEH..."

      Amy went out and got it done, winning the class and two tires for the day. She let me drive a couple of laps in the Mustang in the final TT session at the end of the day, but it wasn't needed, and she won TT3 all on her own Saturday, with just one session driven in anger.

      Amy likes using the curbs, eh? I kept calling her "Curby McCurbison", but there was zero damage

      We put the Corvette back in the trailer since it looked like it might rain again, which was difficult due to the now lowered ride height of the C4, the angle of our paddock spot and the condition of my back. Lots of wood, ramps and cursing later we got it loaded.

      The Saturday night NASA party started at 6pm and we all had some great food and drinks while they handed out trophies, took pictures with the NASA trophy girls, and all that. We also got our 2014 Regional TT3 championship trophy, since we missed the NASA banquet a few weeks earlier due to a different March ice storm (Thanks to Al Gore!)

      Sunday we got to the track at 7:30 am. Unloaded the C4 again to make room for people in the trailer that day (great shelter from wind and sun) and we got Amy ready for TT session 1 in the red car. We forgot to refuel after her stint so I went to grid in TT session 2 with less than 1/2 tank, making it fuel starved badly. With the downforce the car makes and speeds in Big Bend and some other corners making for lots of lateral g-loading, we have to run 3/4+ tank of fuel, minimum. I fumbled my way to a 1:19.8, fuel starving for 3 laps.

      After I fueled up the car fully, I went out again in TT session 3 after lunch, when the conditions were a bit worse. I ran a 1:19.1 in two laps before catching traffic, but by then the front tires were DONE and it was pushing badly. These well used front tires were not good enough for two drivers both days, so I was almost 2 seconds off my 2014 pace (on sticker tires). That's rule # 1 in racing: TIRES MATTER MOST!

      I had a 1:19.4 on day 1 and got it down to a 1:19.1 on tires beyond "end of life" on day 2, so I guess that's some progress? Amy went out in TT session 4 but the tires were all gone by then and the times were off pace. We loaded up both cars onto both trailers by 5 pm and were on the road home by 5:30, tired but happy to have won the class both days. Amy got her first legitimate TT3 win on Saturday, so she was ecstatic. I was bummed about the C4, and my "practice session" 1:25.0 time (good enough for 2nd by only 2 tenths, and it was an ABORTED lap!) was bounced since it was the lone practice session, so I ended up down in 5th place on Saturday using my "smoking, limping, black flagged lap" in TT session 2 on Saturday, bah.

      continued below
      Last edited by Fair!; 04-23-2015, 04:36 PM.
      Terry Fair -
      2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
      EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


      • #18
        Re: Vorshlag Budget TT Build: Project DANGER ZONE

        continued below

        So that means no worthwhile points for the TTC entry, but two solid "100 point days" for our TT3 entry, if we end up having the Mustang all season (it's still for sale). Four fresh Hoosier A7s (in the right sizes this time, yay) were won here, so we'll have fresh tires on the Mustang at TWS in April. The original set of 245mm R7s still only have about 8 laps on them in 2 race weekends and look great, so we'll run those on the C4 again at the next event (only won 2 new tires at MSR-H in this car).

        So the smoking issue and metal in the oil pan can only mean one thing: the the 24 year old LT1 motor needs to be rebuilt. That's two events in a row smoking and/or leaking oil in the C4, and I don't want to get a reputation for that nonsense. I want the motor rebuilt, back in the car, re-dyno tuned, and a track test day completed before #DangerZone goes back to a NASA event.

        The Mustang must have been weighed 4 or 5 times all weekend, but it was never close to being underweight. We gained some weight somewhere, as it was always about 70-90 pounds over the 3802 pound minimum all weekend, but I kept taking ballast out until we were closer. The C4 only made two laps, in two sessions, so it never had a chance to get called to scales. It was well over the 3203 pound minimum, as I kept topping off the fuel tank and the added mass of the front cage section was also present.

        Left: Saturday TT Results. Right: Sunday TT Results

        Official Results:

        Last up, some in-car video from the Mustang, shown below. This was with a suction-cup mount on the windshield, instead of the roll-bar mounted I/O Port mount usually located behind the driver. I moved that to the C4 and should really just buy another one to keep in the Mustang. It makes for a better view and shows the driver issues (flailing around like I usually am).

        In-car video of the TT3 winning lap in the Mustang

        The lap timer fell off it's windshield mount, so I was driving "blind" without predictive lap times. I hate that, and never want to drive on track without the predictive timing from the AiM SOLO. That 1:19.1 lap was a solid 1.8 seconds off my 2014 pace here (1:17.310, still the TT3 lap record) in the same car, but that could just be the difference between a sticker set of Hoosiers vs a very old and worn set. It was still enough for the win in TT3 and 4th fastest for the day in TT. We had 6 cars in class on Saturday and 5 cars in TT3 on Sunday. Amy was quick Saturday but was off the pace Sunday, when the front tires fell off. Glad she let me take 2 sessions in the car, because we needed it. Still won by nearly 2 seconds but it would have been a tenth or two short with her late Sunday times.

        On the photos - we took pics with our Nikon and my potatocam phone, but thanks to MohFlo photography for the shots they got (bought the digital files) and also to Jason Toth for the images he shot. Their stuff was way better than anything Amy or I took (maybe the one above was OK, which was from my potatocam). And the next time I want to bring to cars to race and DON'T bring any Vorshlag crew to help, somebody kick me in the head? That weekend was a lot of scrambling around, and I'm too old for this crap.

        New Motor + Potential Protest?

        Apparently my publicly posted forum build thread got somebody fired up and there has been a protest made to the National level, which I am assured that I will lose. It has to do with a few tubes in our roll cage design, which are deemed performance enhancing. Of course we can remove or re-route before the next event, but I am going to appeal the two issues. If we lose that at least we have time to correct this before the next event - where we could have lost points or gained a DSQ.

        And before some of you call this nit-picking, I'm glad we found out about it before going to NASA Nationals and getting bounced there.

        As for the motor, there are very clear guidelines in the TT rules on what is allowed and what costs points. As usual we will build the next motor to the limit of the rules, within the budgetary constraints we have set, and try not to make any more power - as we are at the limit right now.

        I am also trying to round up a factory 1995-95 LT1 wiring harness and computer, which we can legally swap to if we do the swap completely replacing the 1992 EFI system. This newer computer will allow for BETTER TUNING on the motor, as the 1992 is a one-year-only set-up with very small number of EFI parameters that can be altered. Sean at True Street said the 1993 model year was a big jump up (nearly double the parameters) and the 1994-95 has even more things he can tweak. This will hopefully help de-tune any power we might make with a fresh motor as well as allow the engine run smoother. Still, the fresh TPS sensor and repairing the giant leak in the air intake tube already made a MASSIVE improvement in driveability and smoothness under power at MSR-Cresson.

        That is what is so strange about the last event - the motor was pulling hard and the car ran strong, other than the massive clouds of smoke coming out of the exhaust. What is it they say? A motor runs best right before it blows up! Well this one didn't scatter, so hopefully the stock crank, block and heads can all be re-used when Erik Koeing at HK Racing Engines gets his hands on this 24 year old longblock. I'll have Olof do a compression check before it comes out (next week) and gets shipped to HK.

        What's Next?

        There are a lot of events we will be at in the next few months, but the first time we'll likely be able to run the C4 in anger is June at Hallett. And of course I want a dedicated track test that is successful and oil/smoke free before we go there. The shop is slammed right now and I'm trying to squeeze DangerZone on the schedule to have the longblock pulled.

        We also need to do some.... test fitting of drivetrain parts... for a customer's upcoming C4 build. This will be the first of its kind, ever built in a C4. Its so crazy I can't even talk about it. Gotta finish his C5 build first, though.
        • April 24-26 - NASA @ TWS
        • May 2 - Cars & Coffee Dallas
        • May 3 - SCCA autocross @ TMS Bus Lot
        • May 9 - Five Star Ford Track Day @ ECR
        • June 13-14 - NASA @ Hallett, "Summer Shootout"
        • August 23 - SCCA Solo at Lone Star Park
        • September 4-6 - NASA @ VIR - Eastern States Championships

        Since the C4 is down, we just finished the track prep and loaded the TT3 Mustang in the trailer. Amy and I are about to head down to TWS for the last NASA event ever at this track, this weekend. Its being plowed under soon to make suburbia even more crowded, yay.

        Until next time,
        Last edited by Fair!; 04-23-2015, 04:42 PM.
        Terry Fair -
        2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
        EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


        • #19
          Re: Vorshlag Budget TT Build: Project DANGER ZONE

          Project Update for May 26th, 2015: Its been pretty busy around Vorshlag and I've been buried in the CNC room, but with a bit of extra help in there for the summer I can finally sneak into my office and write a few project build forum updates.

          This Week at Vorshlag for May 8th, 2015 - including a bit on the C4 at the 6:40 mark

          We haven't had time to work on the C4 other than extracting the drivetrain. Again, we only work on our "shop cars" when we have a gap in our customer work schedule, which hasn't existed. So I snuck the C4 in line for a few hours of shop time and had the guys yank the motor and it was sent off to be rebuilt. We've also had more conversations about "the internet protest", which was actually FIVE things, and we're aiming to fix all of those before our next event. I will go over some upcoming car prep and document the issues of the protest in great detail.

          Motor Rebuild Time

          Yep, after 24 hard years this old LT1 has seen better days. Too much crankcase pressure makes for excessive blow-by and smoke, which precludes us from making a lap without a black flag. There's not much to share in this section other than the motor is finally out and shipped to the engine shop, and how that came to be.

          With but 6 weeks until our next event, I couldn't wait for an opening in the shop schedule any longer, so I asked Brad and Ryan to get that LT1 out of the car as quickly as possible on May 6th. Within a few hours the drivetrain was out and the motor was on a pallet, ready for truck shipment the next day.

          After pulling the driveshaft, c-channel drivetrain brace, transmission and shifter out, they could finally lift the motor out of the engine bay. Its a TIGHT fit in there, with a cross brace right next to the front balancer. Its almost impossible to stab the motor and transmission into the car tied together, unlike in some other cars.

          A sharp-eyed reader noticed the "throttle body airfoil" (top right), which we don't have points for. Its coming out.

          The motor was stripped down to the basic long block, it was bolted to an engine stand I had built years ago for easy GM V8 transport. Many LS1s have been shipped on this shipping stand, but this is the first LT1. This frame was then bolted/strapped to a pallet, wrapped in plastic, and all 480 pounds was shipped to the guys down at HK Racing Engines in La Grange, Texas. One thing someone on Facebook noticed in a picture I posted (and called me to warn me about, thanks Dave!) when the engine was out was an aftermarket "airfoil" in the throttle body. With a 24 year old car, sometimes a previous owner's mods get missed. No excuses - this airfoil is coming out. We want this car to be PERFECTLY legally. Squeaky clean. As a business owner in motorsports I cannot afford to be caught cheating in competition, and I'd rather lose a race than knowingly break a rule.

          HK has pulled the top of the motor apart and told me "it all looked fine". By now they should have some .020" overbore replacement pistons, rings, bearings and valve springs ordered, which should freshen things up a bit. I think they will find some broken piston rings when they tear the bottom end apart, since we noted a lot of scoring in the bottom of a few cylinders as well as "too much" ferrous metal grit in the bottom of the oil pan.

          I'm going to clean the living snot out of the engine bay while the motor gets rebuilt

          Erik Koenig is a master engine builder, and also a damned good racer. I raced with him for a couple of decades and he knows how to read a rulebook. I sent him the pertinent pages, we discussed what we can do (and what we cannot) in TTC, and he's all over it.

          Our TT3 prepped Mustang sold in June 2015

          Problem is that I didn't give him a lot of time, so making the June 15th Hallett event is going to be tight... if the motor isn't back in by then I'm NOT racing our TT3 Mustang at Hallett (it is very much for sale!) Yes, this TT3 car has won 4 tires every time we have shown up to a NASA event in the past 2 years, and did so again a few weeks back at TWS - winning by a huge margin after taking only a single lap on Sunday - but that car is out of competition, for me. If you know of anyone potentially interested, please send them to this link - Thanks!

          No more "back up ride" in the TT3 Mustang, as it still has perfect paint that I want to protect for the next owner!

          So, I've already used my "4 drops" in TTC for the regional championship, so if we miss this June Hallett event in #DangerZone I'm just not going to worry about TTC regionally for this year. With our summer break coming, we won't have another NASA Texas event after Hallett before NASA Nationals East, so I will have to go to an out-of-region NASA event or use non-NASA events to test the car before Nationals. I've still not had more than 2 laps in a row in this car all season, dang it.

          Changes Planned To Be 100% Legal

          I mentioned a couple of the things that I was told were protested against #DangerZone in my last post, but have since seen a more complete list of items in an email from Greg Greenbaum, NASA's National TT director. In private correspondence Greg passed on an alarming number of things that some reader of this build thread wrote in about to protest (five).

          As I mentioned before, some are cage issues - three in fact. One was a very picky, gray area issue that I have been "all but told" is allowed on this car, for safety concerns in this narrow cabin. As I showed in a previous post (again, I am hiding nothing) parts of the roof side bars next to my head are a hair outside of the window plane, but otherwise they'd be inside my helmet. I can't sit any lower without going through the floor, either. Its this way or no cage, and after my accident last year I'm not keen on driving un-caged race cars.

          We always tie in both sides of "NASCAR" door bars to the frame, for symmetry and safety. But in NASA TT-letter classes it is +2 points

          The other two cage issues are shown to be illegal in the rules... sort of. First, the passenger side door bars clearly cannot be tied to the frame even though they are allowed on the driver's side (up to 3 places). I read the rule wrong, where it said "drivers-side" I thought "both sides", stupid mistake on my part. It still seems odd that the cage rules would make for an "asymmetrically safe" cage. So our plan of putting a passenger seat in this car and taking riders is out, since we can't make the right side of the cage as safe as the left without taking +2 points (and bumping up a class). Easy fix with a saw and grinder.

          The third and most unclear of the cage protest rulings has to do with the two optional tubes that the TT cage rule above states can be added to the firewall or foot well areas. Our two tubes are apparently placed too high to be called "tire intrusion protection" (but the rule says nothing about tire intrusion, of course, that is something you have to assume). What the rules wording does say doesn't match of what the rules makers meant, however, as I'm told after this ruling that it should read as follows:

          Originally posted by what they really meant to write
          "Two additional attachment points for either two foot-well bars or two bars to the front firewall BELOW THE TOP OF THE TIRE (one on each side) may be added without TT Modification Point assessment".

          The "below the top of the tire" bit was what I was told is inferred in this rule. Shame on me for not knowing that. The two NASA race directors I showed this cage layout to thought we had them in the optimum place, but they were also wrong. So apparently we have to read and interpret the rules then always ask for a clarification for anything (or risk a DSQ at an event). You were warned: there are the written rules and then there are the unwritten rules. Again, this is an easy fix - We will cut those two tubes out, move them down below the top of the tire, weld them back in place, and then be double-secret legal.

          Item four brought up in the protest was our upgrade to 1996 Corvette Base Trim Level front 13" disc brakes, over the 1992-95 BTM 12" front discs. Again, we did our homework and found that all 1996 model Corvettes came with the 13" diameter fronts, which used to be an optional upgrade on base coupe Corvettes from 1989-95 under the Z07 or Z51 options. But since this car is listed on the same line as all 1992-1996 Corvettes, non-LT4, non-ZR1, we can "update" to the 1996 base trim brakes for zero points (normally +2). Yes, its a loophole but hundreds of racers look for loopholes to exploit - that's called racing. Luckily the National office agreed with our documentation here and disallowed that particular protest.

          Shocking Thing About OEM Shocks

          The last issue that is being ruled against (item 5) has to do with the OEM Bilstein vs the replacement Bilstein dampers we used, which I am gonna lose. See, we don't have the points left in our TTC class points budget to add better dampers (+2), so we elected to stick with the OEM units and changed spring rates instead at +3. That was a gamble that some thought was strange, since we could have done double adjustables shocks (which we sell) for +2 points instead of springs (we don't sell the VBP spring).

          This was how the car looked while cornering on the B6 Bilsteins + 245 R7s + stock bars and springs.

          After driving the car on the 245mm Hoosier R7s at MSR-Houston (above), with the B6 Bilsteins and stock springs, then looking at these pictures... I felt the car had too much roll and dive. Sure, we could have gotten some of that dialed out with adjustable shocks ($3350 MCS monotube TT2 doubles), but probably not as much as I'd like. Tripling the front and doubling the rear spring rates made a bigger change, in my view (and I drove it this second way at MSR-Cresson), so we took a gamble and went that route. I will just have to deal with the less-than-ideal damping offered by the stock replacement Bilsteins. Ideally, of course, we'd change BOTH the spring rates and shocks. That is if we had the points budget, which in this case we just don't. ALL the rest of our points are for the tires - because TIRES ALWAYS MAKE THE BIGGEST IMPROVEMENT IN LAP TIMES.

          Tires matter SO MUCH and virtually everything we do to the suspension is just to keep the tires happy

          So, let's look at the OEM shocks. As I stated before, this 1992 model Corvette base model coupe came with Delco-Bilstein 46mm piston monotube dampers at all four corners, and amazingly the 24 year old original shocks were still on this car when we got it. Unfortunately, two of them were blown, which is to be expected after nearly two and a half decades of use and abuse. So we purchased replacement Bilsteins as close as can be purchased today, and put them on for a "zero point" replacement.

          Wrong. Not the original dampers, not legal. This is what the ruling was on item 5.

          continued below
          Last edited by Fair!; 08-05-2015, 06:17 PM.
          Terry Fair -
          2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
          EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


          • #20
            Re: Vorshlag Budget TT Build: Project DANGER ZONE

            continued from above

            Could we have rebuilt the OEM Delco-Bilsteins instead? Sure, but there were two problems with this idea. First, the time frame we had to build this car back in January (2 weeks) wasn't going to give us enough time to have the old shocks rebuilt. While we are a Bilstein Motorsports dealer, we still don't have the $5000 fill rig necessary to refill the Nitrogen charge in this particular style Bilstein (and that's all it works on). Secondly, if we had said we had these shocks rebuilt, who would have believed we had kept the OEM valving?? We make and sell shocks for a living! That would have been the first thing people assumed - shock guys, cheater rebuild.

            These have been sitting in a box in my office since January, in case we were forced to rebuild and use them.

            The proof about what came in the 1992 model base coupes is shown below, which are some pages from GM documents which I haven't shown before (Jason researched and found this cache of GM documents for the 1992 model Y-body). There are hundreds of pages of period documents on this version of the C4, so have fun digging.

            We knew these Delco-Bilstein monotubes were the stock dampers but apparently some folks didn't even believe that. So I'm showing this now, since I was warned that I'd lose a protest even if we put these old blown out shocks back on without showing documented proof of the OEM fitments. Guilty until proven innocent, but I guess with a build shown this publicly I should expect this level of scrutiny.

            After looking for the exact OEM replacement shocks back in January we found that we could no longer buy these Delco-Bilsteins anywhere, for any amount of money. Not from GM, not from Bilstein, and there were no "New Old Stock" dampers available anywhere (if you find any, please send the link my way!). So, from my SCCA background on similar "stock replacement equivilent" issues we "assumed" that a close alternative replacement to the OEM dampers would be allowed. So we looked and found a set of shocks that were the closest and still available new: Bilstein B6 monotube dampers that are listed in the Bilstein catalog for the 1992 base trim level Corvette. These are a whopping $85 per corner, retail, and we paid less that that with our direct dealer account.

            And while I didn't go into this excruciating level of detail before, I hid none of this. We showed these B6 dampers in one of my first posts here, but I didn't show that there are about a dozen choices for the C4 from Bilstein... they make some for the base model, others for the Z51, some for different years, there's a B6 and a B8, and of course fronts and rears. This array of cheap Bilstein monotubes is what we chose from to get the two part numbers shown for the 1992 base model coupe, shown above left.

            These are painfully similar to the OEM Delco-Bilsteins - they have the same 46mm pistons, same 50mm body diameter, the same shaft sizes, same body dimensions, and no external valving adjustment. You can see the details in the images below, which were captured from the "GM Heritage Center" database of records for 1992 model Corvettes at this link.

            I have cleaned up these scans from 24 year old literature published for this 1992 model Corvette, and even highlighted the mention of Delco-Bilstein (its referenced on 6 different pages) and even the dimensions of the shocks. And the swaybars - which are still the OEM units. These Delco-Bilsteins are functionally identical to what we have been using (the $85 B6 dampers), but that's not good enough to be legal as +0 point shocks, they have to be the actual 24 year old Delco-Bilsteins, which we'd need a TIME MACHINE to get a hold of a new set in 2015.

            GM doesn't keep original stock parts on hand for more than 10 years, but they instead have a "generic replacement part number" that supersedes the original 1992 shock part numbers. This replacement part number is shown for all 1989-1996 Corvettes without the adjustable (FX3) dampers. Its a $28 piece of crap twin tube shock that is so dissimilar to the 1992 model OEM damper that its almost funny. Not gonna happen on my car, no way.

            Anyway, long story short - we are now sending the old and blown OEM dampers (shown above) directly to Bilstein, having them rebuild them, and then asking them to include documentation that they didn't alter the valving in any way. I'll have them seal the shocks in tamper-proof tape if they can, too. And someone will probably still accuse us of cheating, oh well. These "cheater" B6 Bilsteins will be for sale here soon after - cheap!

            I wish I could take people for a ride in this car on track with these B6 Bilsteins. Well, with no right seat that ain't gonna happen. Any way, the C4 on these shocks rides like a big underdamped mess at speed. This is not a great set of dampers, not by a long shot. But they are just the closest thing we can find to OEM that isn't leaking. At $85 per corner, you get what you pay for. But that's not good enough - I have to use actual OEM shocks, not OEM replacements, or take +2 points (and move to TTB). And the burden of proof is on the DRIVER.

            Whatever the answers to life's big questions, we're going to make SURE this car is squeaky clean at Nationals. If I get protested over some bullsh*t non-performance hidden rule detail, I'm going to share it here for all the world to see. Hopefully, after this 5 part protest and the resulting changes we will make to 4 items, it will be smooth sailing from here on out.

            What's Next?

            We're desperately trying to get the motor back and installed in time to make Hallett June 13-14, but time is not on our side. I'd also like to get the following changes, modifications and completed before NASA Nationals East:
            • Since my red Suzuka trade fell through after the fact (not my fault), we have to install a new driver’s seat (black Cobra Suzuka GT width Kevlar seat just arrived)
            • Add a massive oil catch can + breather system to the motor
            • Add aftermarket oil pressure, oil temp and water temp gauges
            • Install poly bushings throughout + machine offset Delrin bushings where needed
            • Design and build front brake cooling + new braided brake lines
            • Build support frame for rear plexiglass hatch and install
            • Move full sized battery to rear cubby hole + rewire main battery cable with main power kill
            • Make aluminum covers for ABS and battery cubby holes
            • Take car for interior paint + cage paint, exterior repairs + left side and front end paint
            • Complete the new livery package with stripes #RAMPAGE
            • Spend last point on proper custom cold air and hood venting

            Lots planned before Nationals, and some of it might be protest bait, so we might hold off if it seems unnecessary. Again, the way that the internet protest went down was a bit weird, but look at this build thread - the pictures, the details I'm sharing, the SMACK talk in my first post? I probably should expect this level of scrutiny more often.

            That's all for now - will update once the motor is back! Thanks for reading,
            Last edited by Fair!; 08-05-2015, 06:18 PM.
            Terry Fair -
            2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
            EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


            • #21
              Re: Vorshlag Budget TT Build: Project DANGER ZONE

              Project Update for August 21st, 2015: Its been almost 3 months without an update, and while we have knocked out a few things on the C4, mostly we have just been waiting for the rebuilt motor to arrive. We're less than 2 weeks from NASA Nationals East and I had hoped by now to have the motor in, a few race weekends of tuning under our belts, and ready to go to VIR "fangs out". But a big delay on the motor has crushed our hopes and dreams a bit, heh. Read below to find out where we are on this project.

              But first, in celebration of Grassroots Motorsports magazine's annual "Wear Your Helmet To Work Day" (Aug 21, 2015), I give you our submission we took this morning at Vorshlag. This shows almost everyone here "working" on the 69 Camaro Pro Touring / Track Car we're building for a customer (latest update here). That was fun and GRM shared our picture at the top of their page of submissions on Facebook. Installing an intake manifold on the roof like a pro? I think we nailed it.

              The Best Laid Plans...

              So back in early May I had hoped for a quick 2-4 week turn around on the very basic rebuild on the 24 year old LT1 motor. Paid up front to help speed things along at the machine shop, too. I really wanted to make the June NASA event at Hallett, because if I could have made that event (and scored points both days) we could have salvaged a chance at winning TTC in the Texas region season points battle. We only get 4 "drops" for the year in region, and with the issues we had at MSR-Cresson in March I didn't get any points either day, so that's 2 drops. Then we missed the "last ever" NASA event at TWS in April (we ran the TT3 Mustang for one last time), so that's 2 more TTC drops. Making Hallett would keep us in the points...

              Nope, that deadline came and went. Its been 14 weeks since the motor shipped out to the machine shop, but I keep hearing "pretty soon". Pretty disappointed, and if the motor doesn't arrive in the next handful of days we miss NASA Nationals East (13 days from today). We are moving forward with every hope that the motor shows up, then we can thrash to get the drivetrain reinstalled, get the dyno tune re-checked, install the new Peterson oil catch can (below), then rush out to ECR or another local track for some shake down testing. If it looks good there, then we'll pack up and tow 17 hours to VIR for NASA Nationals East September 4-6, 2015.

              But seeing that we would have to leave in less than 13 days, and I have no motor, I kind of doubt we will make it. Some valuable lessons learned, mostly "take your motor out the day after it breaks" and "use a local engine builder" who is close enough to knock on their door. Daily. Oh well, fingers still crossed. Let's go ahead and cover the work we've done in the past 3 months to this car. Even if the motor returns after Nationals is over, we will still try to make the 2 remaining NASA Texas events for 2015, just to see how it does in TTC before the chassis is re-classed in 2016 (likely to TTB or even TT1/2/3).

              Did want to give a shout out and congrats to Dave Schotz. He took his TTC C4 (built at the same time as our's) to the 2015 NASA Nationals West a few weeks ago and won both PTC ant TTC in his Corvette. He also took the wins in PTC and TTB in his 4th gen Firebird. That's 4 championships in one weekend! Way to go Dave.

              The fact that he won TTC/PTC in a C4 pretty much guarantees that the car will be re-classed next year. So that's not good news for us if we miss NASA East this year. We had one shot...

              Old Shocks Rebuilt and Reinstalled

              If you couldn't tell from my last post where I discussed the "the 5 Point Mystery Internet Protest", I didn't agree with many of the items that were ruled against this car - ruled upon sight unseen, after being protested by a competitor with their name withheld. Oh well, now we all know what to expect when you race in the same class as the _____. (you can fill in the blank)

              We got to spend $450 getting the 24 year old factory Delco-Bilsteins rebuilt by Bilstein-USA. Since we paid for a rush it only took 5 weeks to get them back, hoping that the motor would arrive in that time. Money well spent - these sat around for only 2 more months before we even installed them.

              Biggest difference in the OEM vs OEM replacement Bilstein dampers sets? Blue vs Black dust boots. #CheaterShocks

              We made sure to get documentation from Bilstein, showing that they only replaced the seals and wear items. The original shocks' shims and pistons were left alone. But who cares? Nobody believes anything they read on the internet anymore. These pictures are probably only good for use against me in a future internet protest, hehe.

              Olof swapped out the "new" $85 Bilsteins replacements for the $450 rebuilt 24 year old Bilsteins in 1.27 hours of non-billable time. They look identical to each other, but we didn't bother to dyno both sets to prove how equally pitiful the two sets felt. I'm sure they are just as floaty as the "new" set was.

              8.5 BTM (Base Trim Model) Definition, Updating and Backdating Rules
              For the purposes of NASA TT Modification Points assessments, the term BTM will be defined as follows: Any part that is identical in size, shape, and functional characteristics compared to the part that originally came on the vehicle, from the manufacturer, as a standard feature of the base trim model as it is listed in section 8.2 Base Classifications (factory options and specialty model parts are considered non-BTM) or is listed as a standard replacement part by the manufacturer (OEM).

              Some parts that are produced by aftermarket manufacturers as generic replacement parts may not require a points assessment provided that: they are the same size and shape, and have the same functional characteristics as the BTM part, and that they provide no significant improvement in performance, longevity, or reliability. If it is determined in impound that such a part does not meet the above description, the driver may be disqualified. Consultation with the Regional TT Director prior to competition is advised for any driver using a vehicle with replacement parts that fall under this exception.
              This is sufficiently vague as to mean "we can pick when we want a replacement part to be legal". We learned from this ruling and the precedent set that: unless you are using the original, as-delivered factory base trim level shocks on your TT letter car, you should just take 2 points for whatever shocks you have installed. There is no "OEM equivalent" for these mysterious and mythical parts called "dampers". You were warned.

              Remove Cage Tubes

              Speaking of wasted hours, Olof spent another 2.4 hours taking these roll cage bars out. Yay.....

              Again, I completely disagree that these two optional bars forward to the firewall aren't 100% legal (again, without taking points we didn't have). They were installed as no-points tubes to the letter of the rules, but the "unwritten" wording is what got us. They weren't below the top of the tire, which is true - even if that phrase is nowhere in the NASA rule book.

              These two optional bars connecting the door bars to the frame on the passenger side weren't legal without taking points. I still think its silly to encourage asymmetrically safe cages, but we pulled those two bars out.

              Once the 4 tubes were cut out the flapper wheel on the electric grinder was used to get the stubs of tubes smoothed flat. It took time and made a huge mess, but there's now no sharp edges to catch a driving suit or cut your skin, if snagged. And more importantly, there's no nit-picky visible items to protest. #CheaterCage

              Cutting and grinding the cage to get these tubes out made a lot of metal dust, which went everywhere inside the car, so Olof spent another 1.15 hours cleaning out the entire interior. With some oil that was spilled in the floor on the passenger side (when "Old Smokey" was giving its last death throws at the NASA MSR-C event), and piles of metal dust, it made a real mess. But he got it cleaned out and ready for the replacement Cobra Suzuka GT seat - which is here and going in later today.

              continued below
              Last edited by Fair!; 08-27-2015, 10:39 AM.
              Terry Fair -
              2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
              EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


              • #22
                Re: Vorshlag Budget TT Build: Project DANGER ZONE

                continued from above

                Engine Bay Power Wash + Seat Swap + Firewall Re-seal

                Having the drivetrain out sure makes for a perfect time to clean two+ decades of crud out of an engine bay. This one had it all - oil, dirt, funk, and grease. Brad rolled the car out back and fired up the pressure washer in 105°F heat and got it blasted clean under there.

                Once inside I used my "WD40 all the things" trick to shine up the old painted surfaces and rubber. Let that soak then wiped it down.

                After the cage tube removal mess we cleaned the glass inside and out with Windex and newsprint, to polish the glass. First time I've been able to see out of the glass in all directions without looking through some film of decades-old funk.

                Today Olof installed the new Cobra seat (the red one went away) and then re-sealed the firewall. There is an aluminum panel where the old factory blower motor/heater core box was in the engine bay, and it leaked a bit of oil into the passenger foot well when the motor smokified. That's finally water tight and should be leak free.

                Now we just need a motor...

                Aluminum Griffin Radiator Upgrade

                One of the things I had hoped to do at VIR was take a lot of laps. I have never driven that track and it has a LOT of turns, so I was hoping to make every session from Friday-Sunday, to learn the line and hopefully put in a good time. I was going to take 2 or 3 sets of tires on 2 sets of wheels, too.

                Originally posted by 2015 NASA TT rules
                8.3.I.c.3) Radiator upgrade/shrouding/fascia modification (drilled or cut holes/slots) that only provides increased airflow to the radiator or oil/transmission coolers (without aerodynamic or engine air intake improvement), and/or radiator core support modification/replacement
                To ensure that the car ran smoothly for longer stints on track at VIR, I wanted to upgrade the radiator. This is FREE in TT-letter class, by the way, for all of you rules Nazis looking at this build (see the "No Points Mod" rule above, which is from page 35 of the 2015 NASA TT rules).

                The stock radiator is already pretty sketchy design, with a tiny aluminum core and glued plastic end tanks. They fail over time at the tank to core junction. This looks like the original piece, too. So I looked at direct fit C4 radiators that were all aluminum and beefed up in size. $545 for one, $625 for another, and all of them would take 6-8 weeks to be built. Nope!

                The OEM radiator is bundled with the A/C condenser (already removed) in this fiberglass, factory duct box. It has no filler neck, as the car has a remote coolant reservoir tank higher in the engine bay. The two fans and shroud look sufficient, and don't do anything at speed anyway. I measured the radiator core size and did some searches...

                We used the generic Griffin aluminum radiator for a mockup in the 69 Camaro (left), which fit that frame spacing well

                Summit Racing catalog has 2,312 different aluminum radiator listings just from Griffin. So I picked a NASCAR style Griffin radiator of the same basic height and width, with the same inlet/outlet layout, but with a massive 3" thick dual core. This was a $175 retail part, now we just had to modify it to fit this car...

                Olof then modified the "generic" radiator to fit inside the C4 shroud and frame layout. The lower radiator hose was angled, so that was cut off and the hole plugged. It needed to move upwards a few inches to clear the front cross beam (see below), so he drilled a new hole and moved it there. Then he modified the fiberglass radiator shroud/housing/mount to clear the inlet on the top left corner. The radiator neck was cut off and capped, then a matching "steam line" was added. This was done with a weld bung and re-using the fitting that came with the Griffin, which was threaded into the water neck for the overflow port.

                It worked out great and took a total of 4.05 hours in total for Olof to: remove the OEM radiator assembly, modify the radiator (cutting and TIG welding), pressure test the modified Griffin unit, modify the brackets/mounts inside the fiberglass shroud, and reinstall everything. In the end we got a LARGER capacity Griffin radiator that fits better and is bigger than anything we could have bought that was a direct "bolt in" for the old C4.

                During that 4 hours of work Olof also made an aluminum cover for the gaping hole in the side of the fiberglass box where the A/C bits passed through (visible above left). The new radiator was bigger in every dimension just enough so that it barely fit in the fiberglass enclosure, and there wasn't even room for rivets to hold this panel on - so it was bonded with epoxy and held in place while it dried with the green tape. There were also weather-strip seals added next to the new radiator to better seal it to the inlet/outlet sections of the fiberglass duct - that should be better than the factory airflow management in the radiator box.

                We're really ready for the motor....

                What's Next?

                I just heard back from my engine builder minutes ago, and he says the last "hard to find OEM LT1 engine parts" are finally there. He's supposed to be wrapping up the motor this weekend, then bring it personally to our shop since its so late (no time for pallet shipment). So I'm hoping he's right, and we might, just might, get this car together in time to make VIR in 2 weeks. They need my entry for TTC to "make a class" at Nationals, so others are counting on us to be there, too.

                We had a lot of other plans we would have implemented if this car was put together 2-3 months ago, like we had hoped for. Things that are small incremental improvements in weight balance, airflow, safety, etc. But with virtually no time left to test even if the motor showed up tomorrow we're holding off on more changes to the car. Too many changes means too many risks of something done that fails - and I cannot afford for any failure if we make it to VIR in 2 weeks. I need an uneventful weekend with lots of track time, some good lap times, and no trivial protests.

                Now we just need a motor...

                More soon,
                Last edited by Fair!; 08-21-2015, 05:45 PM.
                Terry Fair -
                2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                • #23
                  Re: Vorshlag Budget TT Build: Project DANGER ZONE

                  Project Update for October 16, 2015: Its been another 6+ weeks since my last post, and it has been a roller coaster ride of ups and downs. The rebuilt motor finally showed up on October 6th and was a week long thrash to try to get the car together for a track test October 10th at ECR and a NASA race weekend Oct 16-18 at TWS. We had already missed the September NASA event at MSR-H so we are really pushing to get the car to the last 2015 NASA event in Texas. Unfortunately things did not go to plan and we're scrubbing this race. Let's cover what has been done since my last update to explain...

                  Note: After writing this update over the course of 2 weeks of work on the car, I had my thread update completed in a private section of our forum - which we use to compose and edit these mega sized build thread posts. Jason had edited everything the night before I scrubbed the event, and the morning I was going to post this (Wednesday the 14th) our forum crashed and has been down ever since. Its so borked that the server is auto-generating 20,000 error message emails a day, driving me nuts, and I have two teams of tech gurus working on fixing it (we've had that forum operational for 13+ years and its never gone down like this). Luckily I had this post open on a window on my pc, so I could copy the text, but it lost all of the UBB code for formatting, images and links. In a rush to rewrite this post now I won't link all my pics to larger images like I normally do and might miss some links I had in here before.

                  You will notice in this series of posts that I'm not sharing any pictures of the inside of the rebuilt motor and censoring some images where those bits are visible. I'm not going to stop sharing pictures in this build thread, as it is still part of showing "what can be done on a budget" and "what race prep we can do" at our shop, but I'm not giving any more ammunition to our competition!

                  Rebuilt Motor Arrives

                  Let's talk about TT-letter class allowable engine rebuild rules. Here they are:
                  Originally posted by NASA TT Rule 8.3.i.c
                  18. Engine rebuild with head shave, block decking and 0.020” overbore provided that compression ratio is not increased by more than 0.5 and displacement is not increased by greater than 1.49%. Forged pistons and internals are legal; however, they must be of equal or heavier weight than the BTM parts, and points must be assessed for de-stroking, and/or increased displacement and compression ratio if greater than the limits listed above. (Note: 0.020” overbore with OEM rods and overbore pistons will yield an increase in displacement of approximately 1.1% for most engines.) If forged internals used are lighter than the BTM internals, then Dyno Re-classing (Section 8.4) should be used to prevent disqualification.

                  19. Engine balancing and blueprinting

                  20. Removal of the engine balance shaft and/or balance shaft drive mechanism

                  21. Non-BTM valve springs and retainers, piston rings, and rotary apex seals
                  My engine builder worked with me at length throughout this build, and sent plenty of images during the rebuild process, but I'm not showing any those here. NOPE.

                  This engine is a NASA letter class legal rebuild, with nothing out of the ordinary. I'm not going to get into the specifics of what we had done to this LT1 engine, but I will say that it was a 100% legal rebuild. No grey areas, no loopholes, just a solid TT-letter class legal engine rebuild that will likely pick up zero horsepower, only reliability. This engine would survive the most brutal tear-down protest. It is also very well built, uses all new parts, and was not cheap. The engine builder even made fun of the fact that we were having to use OEM rockers, pushrods, rocker studs, guide plates, etc. "I've never had anyone ask to use the stock stuff before!" We went over the rules with him in detail, and he is a racer himself and understands how important rules legality can be.

                  The engine took over 5 months to be rebuilt partly because so many of the 1992 model specific OEM parts were tough to procure (this "GenII" V8 engine family was only used from 1992-96 and the Corvettes used different parts than the Camaros or Impalas of this generation), and there were parts changes for almost every year of this LT1 - we can use any 1992-96 LT1 Corvette engine, but only as a complete assembly - no mixing and matching of parts like camshafts, heads, etc. We stuck with all 1992 stuff, but it wasn't necessarily the best choice.

                  There were nationwide searches to find some of the items needed, which took a lot of time. I'm not going to bore you with the trials and tribulations of building a 25 year old motor with many of the OEM parts, but it was a bit of a nightmare. And the engine builder admittedly had some inexcusable delays on his part, but it finally got here as an assembled longblock at the 11th hour, just in time to make the last NASA Texas race of 2015. Yes, this was long after 3 more NASA Texas events passed + NASA Nationals East was missed, which I was none too pleased about. We missed almost the entire NASA race schedule, but we hoped to make the last event here...

                  Parts Cleaned, TB Airfoil Removed, New Plug Wires + Wrapped Manifolds

                  The longblock was placed on the engine stand mid-day Tuesday October 6th and then the washed and cleaned Moroso oil pan was installed with a new FelPro gasket and some RTV. Then it was onto several other checks, then the intake manifold and valve covers were cleaned up on Wednesday...

                  These would be installed after the motor was back in the car, to save time. Some deadlines were looming: be at True Street for dyno checks and possible re-tune that Friday, then out to ECR on Saturday for track testing, then any last minute updates the following Monday-Thursday, then load up and head to TWS for a NASA weekend the next Friday-Sunday. Plus our shop was full of customer cars that all had their own deadlines, many going to the same TWS race weekend.

                  While the guys were putting the LT1/ZF6 drivetrain in the car Wednesday morning, I took the intake and valve covers to Friction Circle Fabrication in Lewisville to have these 25 year old parts cleaned in their UltraSonic parts cleaner. These dirty bits were soaked in the 155°F degreaser solution and agitated for 90 minutes, but they came out super clean. In hindsight we should have scraped more of the burned oil residue off the valve covers mechanically before going in the ultrasonic - would have saved a lot of time.

                  It is a good feeling to know your new engine isn't going to be filled with trash that fell off of some dirty part you reinstalled. And there was some serious crusty, nasty stuff on the bottom of the valve covers and inside the intake. Old, burned-on oil residue plus liquid oil in the intake - from the massive blow-by - which was being pumped back into the intake via the PCV system.

                  When I returned with the cleaned parts, Ryan installed the intake manifold (which was a chore - long story) plus the 25 year old OEM injectors. The stock injectors were cleaned and flow bench tested at InjectorRX in Houston back in August, and as you can see with the test results above, the flow rates were all over the map. Three of the units were also leaking and all of them were clogged before, but after they were (ultra sonic) cleaned and rebuilt they all flowed the same. Good insurance on a set of OEM injectors this old - and yes, we have to use the stock parts here, or take more class points we don't have.

                  The aftermarket throttle body airfoil, which we didn't know was installed until someone noticed and pointed it out from one of my build thread pictures earlier this year, was removed when the intake manifold went back on. The one NASA event where we (unknowingly) ran this airfoil on the car and actually got a class win, we had the points for it (+2 points), as we hadn't done spring upgrade yet (+2). These throttle body "air smoothing" airfoils were super common to run "back in the day" on the TPI and LT1 V8s built from 1985-1996, due to the abrupt shape change of the twin throttle body set-ups GM liked to use back then. Nowadays the LS-series GM V8 engines use a single round throttle blade, which feature smooth inlets and MASSIVE throttle blades (and flow) in comparison.

                  Anyway, the airfoil is no longer on the car, and is sitting on my desk as a paper weight.

                  With the valve covers and intake off, you get a big helping of NOPE

                  Before the motor went going into the car we replaced the AutoZone plug wires with some 8mm Taylor wires made for this LT1 Corvette - these are a bit easier to change with the engine out of the car. The old plug wires were still fairly decent looking, but why chance it when the motor is out? Spark plug wires are "free" per 8.3.I.c.6, for any rules lawyers that are reading, and the costs were around $65. I tend to use Taylor plug wires on everything we build around here. New NGK split electrode spark plugs were also used - we've seen good results from these and they don't have itty-bitty iridium or platinum tips that can fall off.

                  The OEM exhaust manifolds were also wrapped with DEI header wrap before going on, to keep a little heat out of the engine bay. As we've done throughout this build, if it has to come off or for some other reason we have to touch a part, we're going to make it better - to the limit of the rules and within sane budgetary constraints. Header wrapping the manifolds is legal per NASA TT rule 8.3.I.c.23. Ryan used an old hot rodder trick to wrap these manifolds - he pre-soaked the DEI wrap in water, to make the material more pliable during installation. It was wrapped tightly around each tube tightly then secured with safety wire at the ends. The water boils off quickly during start-up, if the wrap hasn't completely air dried by then.

                  Drivetrain Installed + Oil Catch Can/Breather Install

                  The re-installation of the engine is pretty boring work, but it does eat up time. And like everything else, doing this work on a Corvette is more cumbersome than most cars. The ZF6 speed was pressure washed and cleaned up (previously covered in oil from the old RMS leak) before it was bolted to the motor. Everything we touch on a race car goes on clean, even old OEM parts. Dirty parts help hide leaks, cracks and other issues.

                  Assembling the triple disc clutch to the flywheel, stabbing the transmission and hydraulic TOB, and getting everything into the car was handled by Ryan and Brad. It takes more time to line up the clutch plates and get all 6 pieces lined up together, but this is not hard for our crew. A metal clutch alignment tool is a must for these multi-disc clutches, by the way - we use an old T56 input shaft.

                  After the drivetrain is in place, the big aluminum C-channel that connects the diff to the transmission goes in (which also functions as the transmission mount, just like on a Miata), as well as the stock aluminum driveshaft. Then the OEM exhaust system goes in, the stock shifter is installed, various wiring harness plugs are attached, etc. No pics of that as Brad was helping and I was across town. This car still has the original OEM mufflers and catalysts, which we visually inspected very closely before the motor went in - the catalyst matrix is still intact after all these years, somehow. Changing the manifolds, cats, mufflers or even the tail pipes costs points in TT-letter classes, so it all has to stay bone stock.

                  After the engine was in place, we did one more (zero points) upgrade I had planned on for a while, and one we do in a lot of customer's race cars (see above) - add an oil catch-can/crankcase breather. This is something smart to add to any car that sees track time or extended RPM use. The way we plumb these, and how we specify the catch can itself, depends on if its an emissions legal street car (above right) or a track-only race car (above left). A street car isn't supposed to have an open vent for crankcase fuel/oil vapors to get out to the atmosphere, so street driven cars are plumbed with a PCV system to pull excess crankcase vapors out during deceleration and route them back into the intake manifold, to burn them in the engine. Liquid oil in the crankcase vapors is trapped within media inside the catch can, which can collect in the can and be drained out after track days. On a race car you don't have to do with a PCV system - and you don't want to.

                  This is how much smoke was coming out before the engine rebuild... that's all blow-by

                  One of the main problems we had with the LT1 motor in the Corvette earlier this year was tons of blow-by. Combustion by-products getting past the piston rings and valve guides/seals then pushed into the crankcase. This was only realized after the leaking oil pan gasket and rear main seal were fixed before our second 2015 NASA event in this car. The blow-by was from worn out rings, three valve guides that had lots of play, and valve seals that had crumbled over two and a half decades. It was smoking so badly we couldn't make one lap without being black flagged.

                  This is the Peterson 08-400 catch can / breather tank we used

                  Since I didn't want to take any chances after having "that smoking Corvette" for two NASA race weekends this year, I ponied up for a Peterson Oil Catch Can / Breather a few weeks earlier. It has two -12 AN fittings for inlet, a -6 for a drain (which comes plugged), and the built in breather in the cap. Even comes with a nice mounting clamp. So when the motor was back in the engine bay Ryan and Brad mounted the breather can on the firewall, then plumbed some -10AN bulkhead fittings to both valve covers (because that's what fit the OEM hole on the passenger valve cover).

                  One fitting went in the factory PCV suction line on the passenger valve cover but the driver's side cover had to be drilled. We have removed the PCV valve and function completely. These factory LT1 "center bolt "valve covers are magnesium and tricky to work with, but they were drilled handled properly and plumbed with -12 sized push-lock 300 psi hose and -12 AN fittings into the Peterson tank.

                  Now both valve covers vent will excess crankcase pressure to this oil catch can, without the need for a vacuum source to "pull" the vapors out. This Peterson catch can has an integral breather in the lid, which is what makes it not street legal. We have completely done away with the PCV system, so now it is less troublesome and won't allow oil and/or unburnt fuel vapors to be returned to the intake track to be burned - which can cause detonation. And if you get a lot of blow-by it won't send liquid oil back into the intake, which is really bad.

                  First Fire + Weird Ignition System Issues?

                  After the breather tank was plumbed, all of the engine fluids were topped off and some Royal Purple break in additive (zinc) was added to the 10W40 Mobil1 synthetic oil we used for initial break in (normally I like to run 15W50 in race cars). The ignition coil and the fuel pump relay were disconnected, then the engine cranked for 10 seconds, and it made 20+ psi of oil pressure almost immediately. After that the coil and fuel pump were hooked back up, the fuel pump was triggered a few times (key on/off... on/off.... on/off) to prime the fuel pressure in the lines and fuel rails, and then it was cranked. And cranked. And nothing. No start.

                  Then began a full day chasing the starting problems. First we assumed the obvious: it was Optispark related. This is the name for the system GM tried (and failed) at making a better distributor with in the GenII V8s, with a weird unit is driven off the timing gear at the front of the motor. This is widely known as a problematic system. The GenIIs camshaft drives the water pump, also strange, which feeds the motor with coolant in the reverse order of any other motor on the planet. The water pump is right in front of the Optispark, and if any coolant/water gets in the Opti, it usually dies. The LT1's two main bad ideas were the Optispark and reverse flow cooling - they were both abandoned in the next generation engines by GM (GenIII LS1).

                  Checking fuel pressure, computer issues, wiring harness breaks at Vorshlag (left) and True Street (right)

                  The other issue we kept running into was thought to be VATS related, or Vehicle Anti Theft System. There's a chip in the ignition key that tells the computer "Hey, I'm legit!". Without that handshake the fuel pump won't fire. It intermittently worked, so we have to disconnect the battery to clear it up. Something I thought was removed when True Street tuned the car, but the SECURITY light kept flashing. The VATS on my 1999 GMC truck was doing the same random faults a few months ago and Sean from True Street plugged in and turned that mess off, too. GM "VATS" is pretty much a "leave me stranded in my own car" system.

                  continued below
                  Terry Fair -
                  2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                  EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                  • #24
                    Re: Vorshlag Budget TT Build: Project DANGER ZONE

                    continued from above

                    The Optispark previously used in this C4 was an aftermarket $500 MSD unit that had less than 3 hours of use on it, so I doubted it could be bad. Maybe a ground wire was missed, or a wire cracked during the install (from age) on the factory harness? Ryan and Brad broke out the factory 1992 Corvette manuals and went through the Ignition Troubleshooting Flow Chart, step by step. Everything they checked worked, we just didn't have spark. Voltages were checked in the harness and into the Opti at several locations. The coil was swapped out for an MSD LT1 unit we had in the shop. No help.

                    Finally we broke down and ordered a stock replacement $150 Optispark unit from O'Reilys, which showed up 10 minutes later. It was 3 pm the day before our scheduled dyno day and track test, so it was worth the peace of mind.

                    This small victory was short lived - the problem never really was in the Optispark

                    We plugged the new unit into the engine harness, put the coil lead near the cylinder head, and spun the drive on the Opti... pop-pop-pop. We had spark, so it was proven to work. So out came the nearly brand new MSD Optispark unit, which meant the water pump we had just installed had to come back off. Order more gaskets while that's being swapped in. While the MSD Opti it was off the car they did the same "off the car" test and... damn it, the MSD unit worked like this, too. So I had to make the call... put the problematic MSD unit back on or have them install the brand new OEM replacement Opti? I told them go with the brand new unit.

                    By this point we had called and spoken to several LT1 experts and got suggestions from "bad ground", "bad ignition module", "bad ECM" and of course "Its the Opti!" It is almost always the Opti, but I doubted that more and more as we tested the old MSD unit off the car and it came back as good.

                    Another short lived victory - it started with the new Opti, but ran poorly

                    After a long day of troubleshooting the engine and with the new Opti installed, the engine fired up and ran briefly with the water pump off, so that was good. Then the water pump and coolant hoses had to go back on, the coolant get filled (with distilled water + Redline water wetter) and burped again, and the front of the engine went back together - drive belt, intake tube, etc.

                    What should have taken an hour to wrap up that Thursday morning ended up taking all damned day. The engine was finally started, it ran (poorly), the coolant system burped, temps checked out and loaded into the trailer for a dyno test the next morning. It was 7 pm and everyone was glad to go home.

                    Still, it just wasn't running that smoothly. The engine was idling way too high, way up at 2000 rpms, and it had a throttle tip in stumble. Our LT1-expert Ed stopped by and got the set-screw on the throttle blade set to turn ever so slightly and now it would idle at 1600 rpms, but it wouldn't go lower. Hmm. Also, after the engine warmed up, it wouldn't start again easily. It would crank, but wouldn't fire. Something still wasn't right. After 10-15 minutes of cooling down (it barely got up to operating temps) it would fire up, but once it was warm again and we shut it off, then tried to restart it - nothing. Just cranked, no fire. What is going on here? We scoured the car looking for other issues - grounds, broken wires, etc.

                    The guys at True Street had been ready for us to come by mid-day Friday for a dyno check and re-tune, but with the Optispark + other issues, we were delayed by several hours and missed their deadline. I called them at 4 pm and told them we were going to miss that window. Luckily they were hosting a big "dyno day" setup the next morning, so I planned to get there early and be first in line.... then head to ECR for a member day track test right after that.

                    Dyno Check at True Street, Saturday October 10, 2015

                    Loading the car into the trailer with a triple disc clutch is a PITA, but we hadn't stopped long enough to make front (or rear) tow hooks for this car. So when we got to True Street Motorsports at 8 am Saturday morning, an hour before they opened, Amy and I just rolled the car out of the trailer. Then I tried to start it...

                    NOPE. It cranked like a champ, but once again the coil wasn't firing. It won't start now, even cold. We fought with it for a solid hour, clearing the battery and trying again and again. It got to where the battery was losing voltage, and it still wasn't starting.

                    I thought about asking the guys at True Street for a hand, but they were all busy getting their shop cleaned up and ready for 200+ people, who had started arriving in droves. They had a food truck setting up, and cars starting to get dyno'd when we decided to abort the dyno test and load up.

                    Missing this open track day at ECR was a huge disappointment, and it put me in a foul mood for the rest of the day. I knew we would have to spend more (unbillable) hours the next week to get the C4 running "right" and starting consistently before going to NASA @ TWS the following weekend, without any test time on track. With a new motor, new radiator, and new crankcase breather. Testing this many new things during a competition weekend sounded like a bad idea, and it is.

                    More Testing At The Shop + True Street

                    Monday morning we unloaded the Corvette at Vorshlag again and Ryan and Brad spent most of the day tracing circuits and testing everything, wiggling the harness, and looking up issues with these cars. More and more evidence started to point to a bad ECM - the 25 year old engine computer might be at fault. My ops manager Steve started chasing down replacement 92 Corvette ECMs and that search went well into Tuesday. He called dozens of wrecking yards and LT1 re-programmers, parts suppliers and GM dealerships across the country. Nothing, nada, zip - no 1992 Corvette ECMs anywhere.

                    Just to eliminate any last "part problems" we ordered a new ignition module and replaced it. This was mounted it to the coil/module bracket with proper Heat Sink Compound. Then we spaced the module + coil bracket away from the cylinder head for heat protection from the engine. No change.

                    Sometime around mid-day Ryan had done some sleuthing online and found a number of 92 Corvette owners with eerily similar problems. One suggestion was to remove the PROM chip inside the ECM housing and re-seat it. Another said to "whack the ECM a few times, hard!" After doing those two things the car started up again, but still ran a bit rough. More tests were done, but it at least ran. We called True Street, who were backed up with tuning work for 3 weeks... I begged, and they agreed to call me back if they had an opening. As luck would have it they had a last minute cancellation and were able to sneak us in for a dyno check-up. I towed the C4 up there Tuesday after lunch and they got to work.

                    After I left, it wouldn't start again. Sean played with things, checked some codes, and late that day they had found a bad TPS sensor. With the TPS unhooked it would start, but you can't drive the car like this. We had replaced the TPS with a new sensor back in February, after I noticed a weird "throttle dead spot" at the January NASA event. Hmm... red flags were going up.

                    I spoke with Paul Costas later that night and told him the symptoms we were having, and he related a similar issue he had on his 92 Camaro (which is a GenI TPI V8, but used a similar vintage computer and EFI tech). About a year ago 92 started running poorly and burning up TPS sensors. He talked to an EFI expert familiar with this vintage GM EFI hardware, who said when these ECMs go bad they often lose their reference voltage outputs for 5V circuits like the TPS (Throttle Position Sensor) and IAC (Idle Air Control). He told Paul to test voltage signal at the TPS while driving... and sure enough it spiked way above 5 volts several times, which was what was burning up the sensors.

                    And we've just burned up another TPS sensor, and the car had a weird throttle response issue when it would run. And the idle was super high (IAC circuit) at some points. I was more convinced than ever that the ECM was dying and emitting some weird reference voltages. But with no replacement ECM for this car to be found nationwide, the chances of making TWS looked slimmer by the hour.

                    I was stewing over this for days and mid-day Wednesday I decided to scrub the TWS event. We had ECM problems and there was no way to fix it in 24 hours we had left. Crap, crap, crap!

                    What's Next?

                    Long term plans had always been to convert the car to a different ECM and harness from a later 1993-96 Base Trim Level Corvette. There were some EFI changes through the 1992-96 LT1 Corvette era which included:
                    • 1992 was the first year of the TL1, speed density air metering, and had the weakest computer with the least number programmable inputs
                    • 1993 was still speed density but had a more powerful computer with more inputs to alter
                    • 1994-95 was another step up in inputs and computing power with the added change of a move to Mass Air Metering, but still OBD-I. Yet these can be reprogrammed via the OBD-I port, no more E-PROMS.
                    • 1996 was another big change, such as the move to OBD-II standards, the ECM had a significantly more powerful processor, a LOT more data channels and programmable inputs, and also no longer relied on an E-PROM to change programming.

                    Checking with all of the parts suppliers we use it appears that new AC Delco ECMs for the 1996 Corvette are readily available, and around $200 (with the core charge). The other years are "iffy" or just downright impossible to come up with reliable units. So it looks like I am going to be chasing down a good 1996 LT1 Corvette engine harness, ECM, Mass Air Sensor, and intake tube next. We could not hope to pull this off in the one day we had remaining before TWS, so that event had to be scrubbed.

                    We had ordered new R7 Hoosiers, procured a 2nd set of wheels (for the scrub set of tires), event fees were paid, Amy had taken off work, arrangements for the weekend were set, and lots of money thrown at ignition parts that weren't bad - but hey, "that's racing."

                    Some of you might question scrubbing this 3 day race weekend - since the engine "technically starts" now. Sure, you can unhook the TPS and it might start, but it cannot be driven like this in anger. It is not reliable, and will almost certain break and/or run poorly once we get this thing on track. If we plug in the TPS it will burn that sensor up in short order.

                    I'm not giving up on this car, and it will likely be run in 2016 up until our "Shop Car" LSx BMW is complete. So look for us at NASA events in January and more likely some TEST EVENTS before then, to verify the new engine and ECM changes we have in store. My next update will be after we make the wiring harness and ECM changes.

                    Terry Fair -
                    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                    • #25
                      Re: Vorshlag Budget TT Build: Project DANGER ZONE

                      Project Update for January 5th, 2015: Its been a couple of months since I touched base on the progress of Project #DangerZone, our 1992 Corvette race car, and a lot of little things have happened - both to the car and to the NASA base classing rules for 1992-96 Corvettes. We've made some updates to the C4 to hopefully make it lighter (pre-ballast), run cooler, and more importantly - be more reliable once it returns to track use later this month. The C4 is also looking like my only primary race car for 2016, so we're getting a bit more serious with prep on this car and might add a few other racing groups to run the car in. There's only 3 weeks until the next NASA race we want to make in this car (NASA @ MSR-Houston event Jan 23-24) plus a test day at MSR-Cresson the weekend before (Jan 16th at MSR-C). I'm only going to cover the work completed up until now then catch up on the finish work before these two race dates in the next update.

                      NASA RULES CHANGES

                      As some of you might know we've started a BMW E46 330Ci build for NASA TTD class. That project has gobbled up some time and we switched chassis before we even began major race prep on the first car (325iC), which slowed us down a bit, but it was the right move going from the 325 to a 330 (the latter of which was classed better and makes a lot more power). You can read up on that car here, which we've named Project #JackDaniels. I explain the name in that thread.

                      Normally in December of each year, NASA will release an updated rule set for Performance Touring, Super Touring, and Time Trial classes - all 3 of these groups use essentially the same set of rules. PTB-PTF wheel to wheel classes equate to TTB-TTF and ST1/2/3/U equate to TT1/2/3/U. Sometimes the rules aren't published until after the first of the year but this time the 2016 NASA TT rules came out on time, with nearly 8 weeks before our January 2016 event.

                      The C4 listings above are what we built this car around, and those haven't changed in many years (we know because we have been eyeing this car for TTC for 4+ years). But due to how well Dave Schotz did at NASA Nationals West in his PTC/TTC C4, and how much we riled up a few folks with our forum build thread (even though it really only completed one race weekend), we were expecting either a points penalty (*), class change (TTB?) and/or minimum weight change (increase) to these C4 base classes. So here are the 2016 changes...

                      All changes from the previous edition of the rules this year are shown in blue. As you can see the minimum weights for 3 of the C4 models were changed, all higher, including our 1992 LT1 base model. We have to add 57 pounds to our weight or else take points for weight loss, which gets expensive. As you may know we had maxed out this build on points from the beginning. Somehow I never really covered that in this thread...

                      This post on our E46 TTD build thread explained in great detail how we came up with the classing, tire size/compound, chose modifiers and found rules exploits for both the TTD car and this TTC car. I won't repeat what I wrote there in total but if you care to learn some of our secrets, please go here and check it out.

                      Here is a quick summary of our TTC class build for this 1992 Corvette, based on the old 2015 rules. After we saw the base classing (TTC*) and weights we looked at the Power-to-Weight (P-to-W) ratio assigned to the class (12:1). The * cost us 7 of the 19 class points we had to spend, so we have 12 to play with to stay in TTC. Then we looked at the base tire assigned to the class (255mm). Going up in size costs points, down in sizes nets points back. From there we looked for modifiers to the P-to-W ratio... and found a big bonus (+0.8 ) if we ran a small 245mm or smaller DOT tire (see Appendix B in the rules). 1 point was also gained back because that's 10mm below the TTC class starting tire size of 255mm.

                      This modifier effectively moved the P-to-W from 12.0:1 to 11.2:1. Luckily the stock LT1 motor could still hit that revised P-to-W limit without any power modifications. This meant we didn't have to burn class points on exhaust or headers or camshaft swaps or intake mods to max out P-to-W. We spent ALL of our remaining points on suspension changes (springs at +3 points) and tire compound (R7, +10 points), plus our point gained back for 245s (-1) and it worked out to the 12 point mod limit for TTC with maxed out power limit.

                      Let's show those P-to-W calcs "the NASA way" for our TTC Corvette:
                      • Weight must be at or above the listed minimum classing weight of 3203 pounds, from the 2015 rules
                      • That 3203 number is also just above the minimum "competition weight" modifier numbers, which start at 3200 pounds
                      • We chose a 245mm width DOT legal tire (+0.8 P-to-W bonus)
                      • The stock engine made 284 whp peak (highest of 3 pulls)
                      • 3203 lbs / 284 whp = 11.28:1 (P-to-W) + 0.8 for (245 tire modifier) = 12.08:1

                      TTC Class "minimum" adjusted P-to-W is 12.0:1, which this car is just a hair over. That's what you want to do - aim for the P-to-W limit and find any modifiers you can to help that ratio along the way. Avoid modifiers that hurt, then use your points to run the best tire compound/width and fix any suspension issues, and add aero if you have any points left. Again, this is more detailed in the E46 TTD thread, linked above.

                      So that was our TTC strategy for this C4. Now we have to recalculate for the higher 2016 minimum weight bumps, which honestly aren't that bad and are not unexpected. I have to agree with these changes, even if I don't like them. This will mean we have to run even more ballast on the same 245mm tires, which worries me. We haven't dyno'd the fresh LT1 motor but I'm also worried it might make too much power, even at this higher weight (and with the 11.2:1 P-to-W ratio we can now make 291 whp). Even with it only running briefly due to the ECM issues it felt STRONG - and yes, it was a 100% legal engine rebuild. We shall see soon enough.

                      Sadly our E46 TTD build gained a 7 point penalty with the 2016 rules, which I'm not at all happy about. Really borks the planned build. So of the very few changes made in 2016 both of our TT-Letter builds were impacted. I'm just that lucky, I guess.

                      BRAKE COOLING MODS

                      Meanwhile in last two months, before we got the new 2016 rules, we have been working on some reliability mods to the C4. Of the 2 race weekends we ran this car I never managed to make more than 2 laps in a row. So the stock Z51 brakes haven't been pushed hard enough to overheat, but I'm worried they will be taxed once we get the car on track without a leaking or smoking engine. Why worry? Well because I'm a Left Foot Brake fanatic (learned in my autocross background) and I tend to abuse the crap out of brakes.

                      With an R7 tire compound I don't have to get my best laps in on lap 1 or 2 like we did on the A7s in TT3 last year, so yea... brakes might become an issue. So one day when we had the C4 up in the air for harness removal (see below), I asked Olof to pull apart the front brakes on one corner for a better look. We had built brake backing plates with cooling ducts for a C4 before and he kept the templates we used that time, so this shouldn't be a whole lot of work.

                      After he made a flat plate that fit around the hub we discussed where to route the hoses, what sizes to go with, and what shape for the duct at the backing plate. We decided to use 3" oval tube for the inlet, aimed at the hub and inside the rotor face. He built these 2-piece backing plates below.

                      With only a 13" rotor there wasn't room for a 4" duct, and with the track performance of this car a 3" cooling hose should be enough. Now there's also lower piece to this backing plate added to help seal off the hub section so that the incoming air goes where we want it to. It also allows for a bit of a heat shield from a ball joint that is very near the inside rotor face, shown below.

                      The spacing from the backing plate to the rotor face (shown in the picture above right) is what we try to stick with, which allows a decent seal to the incoming air but shouldn't ever rub. The goal is to turn the rotor into a centrifugal air pump, with the incoming air forced into the hub area inside the rotor and the curved vanes of the rotor pulling air through the rotor and out radially. This can increase effective braking during a session considerably, as well as extend brake pad and rotor life substantially.

                      As you can see above left, even the oval shaped 3" duct doesn't put the incoming air completely inside the rotor face, but its as close as we can get without nearly flattening the oval shape. Another thing that we did while the hubs were off was install extended length 3.25" ARP wheel studs. We couldn't find a bullet nosed ARP stud any longer than the itty-bitty stock studs, so we'll just have to start each lug by hand with this fully threaded ARP (it's not like we're doing fast pit stops). The reason why I wanted long wheel studs will make itself known in my next post.

                      While doing the front stud install we would normally swap in new hubs at the same time, for other cars. But for the C4 we kept the original front hubs - they were still low mileage, still felt tight, and the aftermarket options are total CRAP for this chassis. The only good aftermarket replacement hub for this car worth using is a racing hub made by HPE that costs $699 per corner, and I'm not sure if their solution is even TTC legal, so we'll keep the stockers on there for as long as we can. Brake cooling aimed at the hubs tends to extend their lifespan quite a bit on track, too.

                      Backing plates are only 1/3rd of the brake cooling solution - you also need INLET ducting at the front of the car and then brake hoses to join them. After looking at the front end of this C4 I wanted Olof to "keep it simple". Why? Well we're likely replacing the bumper cover later in the 2016 season since the stock cover is pretty beat up. We had discussed about re-purposing the turn signals, adding NACA ducts in the old headlight doors, or even NACA ducts under the front bumper... but I wanted to keep it very simple. "Just make a 3 inch round tube and a flange", which is exactly what he did.

                      Remember - this might not be the permanent inlet duct solution, just a quick one for now. The inlet ducts were relatively easy to make and I had a specific place I wanted them placed. The front of the C4 has a LOT of "front overhang" (see above) where the nose pokes out about a foot in front of the factory front lower air dam (the air dam feeds air to the radiator). All of the radiator cooling is drawn in from under the giant overhang, but there is still some dead space on both sides of the radiator inlet that goes unused...

                      continued below
                      Terry Fair -
                      2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                      EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                      • #26
                        Re: Vorshlag Budget TT Build: Project DANGER ZONE

                        continued from above

                        That's where I had Olof place the inlet ducts. "Just drill a 3 inch hole and bolt them in right there", I told him. The inlets are directly underneath the factory headlight holes, taking in high pressure trapped under the nose that isn't being fed to the radiator inlet. There's ample room under the hood (with the flip-up headlight assemblies gone) to route the hoses up and over to the brake backing plates.

                        Due to concerns Jason and I both had about air pressure bleeding off laterally towards the edge of the nose and bypassing this brake cooling inlet, I had Olof make a little aluminum "brake canard". This is a little air dam that forces some air into a closed pocket to feed the brake inlet. Yes, I know this might incur some aero penalty for TTC. We are going to test with and without these in place and we will add rivnuts in place of the rivets used to attach these little air walls, so we can test with and without them installed.

                        The brake hose routing looks fairly straightforward, but of course we haven't tested it on track yet. It might rub the wheel at full lock, but since the car is still in the air with the wheels off we haven't checked that yet. A piece of the plastic inner fender liner was trimmed to route the 3" hose below the top of the wheel, but we will see how it fits when the wheels and tires are mounted and its back on the ground.

                        Last but not least the car is getting a new set of factory lower air dam plastics. Again, we bought these many months ago just never got around to it. The old bits are beat up and the left sides is held on with Gorilla snot and is half falling off. The new air dam bits will help push more air into the waiting duct for the radiator or the two brake inlet ducts.

                        POLYCARBONATE REAR HATCH

                        Another piece I had purchased way back in January of 2015 that never made its way onto DangerZone was a pre-formed and pre-cut polycarbonate rear hatch from Five Star Bodies. This 1/8" thick, pre-trimmed, formed rear plastic glass was to replace the 46 pound OEM glass rear hatch section.

                        Removing weight was the primary goal, but with our new 2016 minimum weight numbers going up now this might not make as much sense.

                        Of course we did this before the new weight numbers came out, heh. Oh well, being able to move weight from up HIGH (stock glass) to down LOW (ballast) is always a good thing. I'm eyeing that 80 pound hood as well.

                        Once the glass was removed from the factory hinge at the back of the B-pillar factory roof structure, Olof drilled two matching holes in the trimmed-to-fit and pre-bent Plexiglass. Then he built a frame to give it some support at the lower front corners out of thin wall 1/2" tubing. The two Quik-Latches just arrived and those will take the place of the (broken) rear hatch release. Now we can get into the rear area without crawling through the cage and yanking the emergency release cable in the back.

                        WINING HARNESS & MAF CONVERSION

                        So if you've read this thread before you know we had some trouble with the original 1992 ECM (Engine Control Module, or computer) after the rebuilt motor went in, that caused us to miss our last NASA race of the year - the car wouldn't start reliably. After days of diagnosis and parts chasing we had finally realized it was a bad ECM. Well we cannot find a new 1992 ECM, anywhere on the planet. 1992 Corvettes had a "one year" ECM - 93 was different, 94-95 was different again, and 96 was also unique. There are no 1993 ECMs left either, but back in October we found plenty of 94-95 Corvette computers available, both new and rebuilt, and our tuner said the later computers were easier to tune for track use. So the quest to convert this to a 1994-95 EFI harness was underway in October.

                        Instead of trolling junkyards for 20+ year old Corvette engine harnesses, which will bound to have some cracks and wiring breaks, we had a new one built using our 1992 OEM wiring harness for layout. We found several breaks in the existing 1992 harness already - which makes for nightmares when diagnosing EFI issues and the way this one will be built will be the perfect OEM replacement - 100% stock in form and function, just not with 25 year old wiring and broken connectors.

                        We had to find 1994-95 MAF, intake tube and other small parts to convert this car fully

                        We are trying out a new harness supplier, but they assured us it will be identical to an OEM 1995 Corvette harness and plug in, no issues. As long as it mimics the OEM harness and we use an OEM 1994 or 1995 ECM, this should be a zero-point change, as all 1992-1996 LT1 Corvettes are listed on the same line.

                        The harness took a few hours to label the connectors (any emissions or cruise control related connectors will be removed, which again, is legal for TT-Letter) and disconnect everything all the way to the ECM and firewall, and even some bits that went down to the ZF 6-speed. We should hopefully see the replacement harness by the end of this week, which will give us just one week to get the engine dyno-tuned again before an upcoming track test at MSR-C on January 16th.

                        That's what the engine bay looks like now, above left. The 1992 harness was been shipped off weeks ago (they have to re-use some connectors, which are not being made any longer) and it will look like the 1994-95 engine bay soon (above right). We already have an OEM replacement MAF and intake tubes, shown there. Luckily this 1994-95 stuff is available and not costly (new Delphi MAF was about $100).

                        I will show this all wrapped up and hopefully running well again in my next post.

                        WHAT'S NEXT?

                        Since this was only a partial update I'll have another that will show the completion of all of the above work (hopefully) posted after the next NASA event. That assumes a lot of things happen in a timely fashion over the next 2 weeks and that our test at an SCCA Club Trials event goes off without a hitch.

                        Sadly these were the only two tracks we ran the Corvette at last year, but we'll be hitting them back-to-back weekends in January 2016. This time the car will have a newly rebuilt engine, no fluid leaks, better engine and brake cooling, and hopefully some reliability. There were major issues with the C4 at both tracks in 2015 - a leaking rear seal at MSR-H kept us to 1-2 lap stints before we were black flagged, and oil smoke from a worn out engine kept getting the car black flagged at MSR-C in one lap or less. No more of that nonsense!

                        We ran a 1:43.7 lap at MSR-H in 2015 (still the TTC track record) and hope to better that by a good margin this year. We never got an official time in TT at the MSR-C event but, but I did run a 1:25.0 in the TT Warm-up session, which was my only complete lap of the weekend in that car. That was 2 seconds faster than the old TTC record at the time, but another TTC car reset the record on Sunday to a 1:24.424 (Mark Schnoerr's E36 M3). Hopefully #DangerZone can go quicker than those times at both tracks? The SCCA Club Trials event doesn't really have "classes", per se, but it will be a good practice for when NASA comes back to this track in March 12-13, 2016.

                        That's all we have planned so far for the 2016 season - after the January SCCA and NASA track events we will see how we stack up in class for the year and go forward from there, either with refinement or possibly even changes to move to a new class (if the added TTC weight is a big hindrance). We will also have Amy's red 2001 BMW 330Ci at these two events, which is the new #JackDaniels TTD classed E46. For the C4 we have to have the rebuilt harness installed with a 1994-95 ECM (of course now there are none to be had, ugh!), the engine re-tuned to work with the 94-95 MAF, the Plexiglass rear hatch painted and latched, the front brake ducting wrapped up, and maybe some other small changes if there is time. Check back in a few weeks to see if some what happens...

                        Terry Fair -
                        2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                        EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                        • #27
                          Re: Vorshlag Budget TT Build: Project DANGER ZONE

                          Project Update for January 22nd, 2016: Well the C4 has logged a successful test track day in 2016, where we tested a lot of big and small updates to this car (and a new BMW we're running in TTD this year). There was one fairly big change with Project #Dangerzone that we have been holding back - because, honestly, I didn't know if it would work. I will explain "the what, why and how" below. We also finished lots of little prep work to this car, installed the rebuilt wiring harness and 1995 ECM + MAF, got the stock rebuilt engine dyno'd (twice), added some tow hooks, fixed the front air dam, finished the brake cooling and rear Plexiglass hatch, lost some weight, and more.

                          After my last thread update I was posting the above pictures on social media with captions like "almost finished" or "finally track ready". This was somewhat of a disinformation campaign, which might help me if I ever run for president, hehe. Gotta keep you guys guessing a little, but the big reveal is shown below. Let's get caught up...


                          In my last update I showed the slightly unfinished work on the lightweight polycarbonate rear hatch replacement. Shortly after I wrote that, our guys got it painted and installed and it looks good.

                          The rear frame was made from thin wall 1/2" steel tubing, which is tricky to bend. This structure forms a frame that wraps around the back glass in 3 axis. Olof welded some tabs in place for the small diameter Quik-Latches that secure the bottom of the hinged rear glass, as well as tabs for the hinge mounts at the top.

                          The mating pins for the Quik-Latch kits were installed in some simple brackets that Olof built and attached inside the rear of the hatch opening. Not only did the heavy 46 pound glass go away the big, electric solenoid operated, clunky steel latch mechanism also went away. The optional spring kits were added to the QuikLatches and that made them work a lot better. The rear frame was painted while hanging on a rack, and I snapped the pic in front of the LS1 Miata - which is about to get a big project thread update. We neglected to snap a picture of the final weight of the Plexi hatch and frame, but it looks like we lost 30-ish pounds - the new hatch is super light and much easier to lift.

                          I had the guys paint the back of the plexi around a ~3" border, to give it an OEM look. Trust me, its worth the time and makes a helluva difference. Brad and Olof taped up and covered the area not to be painted then peeled the protective covering from the inside of the Plexiglass (both sides come covered in a protective film). The clear plastic was scuffed with ScotchBrite then cleaned and let dry. Then it was painted with two light coats of semi-flat black.

                          The painted hatch was then allowed to dry, after which time the frame was bolted to it on the inside and the QuikLatches installed. The frame was bolted to the factory hinge using the same stainless washers and flush head bolts we use on all Lexan window installs. The latches lined up and the spring poppers were added to the Quik-Latch assemblies.

                          You have to see it in person but the finished hatch looks really good. Going the extra yard to paint the border (on the inside) makes it look so clean and factory, covers up the steel tubular frame inside, and finishes off this mod well. The Quik Latches work great and we can access the rear hatch easily now (before you had to crawl through the back of the car and pull a cable - total PITA).

                          1995 ECM, MAF & HARNESS INSTALLED

                          Updating the ECM and harness on this 1992 Corvette was the least fun part of this project to date. What a giant hassle, but the old 1992 computer can no longer haunt us, the engine runs now, and we learned a lot about the differences between the 1992-1997 LT1 engines & cars.

                          Just finding a used 1995 Corvette Engine Control Module proved to be difficult, as all of the sources we saw that had them in stock back in October had dried up. Lots of calls, emails, and finally the guys at True Street told me about a possible source. We paid too much ($315) and its a used ECM (not "reflowed" or rebuilt), but they do program the VIN # into the ECM for us and ... well... they had them in stock. Since it came pre-programmed at least it worked on their bench harness, which is a plus. The VATS would be turned off so the engine could run with our key, too.

                          You can see how different the 1992 (left) and 1995 (right) ECMs look. This is why we needed to have the harness rebuilt - to fit this entirely different pin-out for the later model ECM.

                          Here you can see the Delphi replacement MAF (Mass Air Flow) sensor, which is part of the later 1994-96 Corvettes' EFI systems. The online resellers show the same stock replacement part from 1994-2001 Corvettes with prices from "cheap" to "not as cheap". These sensors have a "hot wire" that sits in the intake airflow path, voltage is applied to this, some wizardry is used, and the amount of airflow is measured more directly. The 1992-93 Corvettes used a "speed density" method of airflow measurement, where intake manifold pressure was used to infer the airflow. The MAF cars still use the old intake manifold pressure sensor, but use that data for fine tuning, not engine airflow measurement.

                          New intake hose ends were needed on either side of the MAF sensor to connect it to the air box and throttle body. The sharp eyed among you might realize that these are not OEM replacement rubber bellows, so they aren't technically TTC legal without taking 1 point for an aftermarket "cold air". There's a reason why this doesn't matter that will soon become apparent.

                          Going from the jumbled harness right out of the box at left to the completed and running engine harness install on the right took a few days, mostly chasing down "old car things". First it was the O2 sensors, which are different on the 95 vs the 92 (went to a heated, 4-wire O2 @ $29 each x 2). Then there was the IAC valve changes. The rebuilt harness was setup for the 95 Corvette computer and they updated the ends for all of the 1995 era sensors, too. Cheap, easy fix that will likely work better than the old 2-wire O2 sensors.

                          Next was the computer itself, which had such a different shape that the (complicated) fiberglass bracket made to hold it was different. So Steve called up a salvage yard in Waco we know that keeps a lot of C4 Corvettes and he got this new bracket for $40, which arrived the next day. Could we have built one? Sure, but the shape and how it mounts was complicated enough that making one would have taken an hour or more, and every hour we're spending on this shop car is an hour we're missing out on customer work. $40 for the factory piece was the right move here. Remember: even though you can make something from scratch, doesn't mean that you always should.

                          Yet another "learning more about 25 year old LT1 engines" thing here - the Idle Air Control valve (IAC) is an electronically controlled device that meters air around the (closed) throttle blade, so the car can idle with your foot off the throttle pedal. GM changed the mounting shape and the 4-wire connector for the IAC from the 1992-93 LT1 cars to the later 1994-97 LT1 cars. The way the IAC mounts to the throttle body is via a small "manifold" (above right) that bolts underneath. As far as I can tell the throttle body didn't change much, so we just needed this 1994-97 IAC/coolant manifold, which bolted to our 1992 throttle body.

                          After a full day searching we realized this part wasn't available new, and even Nook & Tranny was out of stock (they carry a lot of LS1 and LT1 stuff - helpful website for engine swappers). It was late in the day when we realized how scarce this manifold would be, and our Waco Corvette salvage yard was closed by then.

                          So we started looking for LT1 throttle bodies locally... my Facebook call-out was a miss but someone there suggested a junkyard here in town that had one for $50. So the next morning, the highlight of my birthday was trolling around in the bad part of town and grabbing up this 1996 Camaro throttle body. Ryan cleaned up then transferred over the IAC/coolant manifold and the new 1995 Corvette IAC ($53) to the 1992 throttle body and it was ready to fire. Curiously the shape of the throttle blade cable pivot cam was very different from the Camaro to the Corvette parts.

                          TOW HOOK + FINAL BRAKE DUCT ROUTING

                          We've not had good tow hooks on this car, which is pretty short sighted for a track-only car. This is one of the first mods usually done to a race car, and we were lucky we never had to be flat towed in at the track, because there's not good places to latch a tow strap onto in this car. The front of this car is all plastic and there's nowhere good to bolt or mount a tow hook, so we had to get creative.

                          We figured out on a previous C4 race car how well a roll cage mounted top tow hook works, for both winching a car into a trailer as well as for towing behind a wrecker. The top hook eye Ryan added to the cage also works as a great grab handle to winch yourself into the tight cabin of a C4. It will be easier to get into this car once I have sprung for a Quick Release and a real steering wheel, but for now this works great. Have already used this new hook to winch the car into and out of our trailer multiple times.

                          Ryan also installed this roll cage mount "bus stop" mirror, a low cost convex mirror that lets you see into blind spots. We already have a 14" wide parabolic rear view mirror mounted in the cabin, but the right side factory door mirror broke decades ago, and the FIA cage tube on that side blocks my sight line to it anyway. This new spot mirror fills in the right side visibility gap from the side window to the high mounted rear view mirror perfectly. Bolted on in minutes and the old, dead door mirror housing was removed (less drag).

                          The guys also got the final routing of the 3" brake duct cooling hoses nailed down. There's a number of zip ties that attach the hoses to moving suspension components, like the upper control arms. And some that hold them to fixed items inside the engine bay.

                          These hoses even clear the 335mm tires on 18x12" wheels up front at full lock, so they really got them tucked in there nicely. Oh yea... did I forget to mention the little wheel and tire upgrade??

                          BIG TIRE TEST

                          What and why have we changed from the 245 R7 tire to a 335 front and 345 rear Hoosier A6?? Well let me try to explain. And remember, this was only a test - it might have been a complete disaster and I would have un-done the work and slapped the TTC legal 245s right back on.

                          Last year we only built this Corvette to run for one season as a "tweener car", after the TT3 Mustang was sold and before our next big crazy shop BMW V8 build was ready. Well we never started that big BMW build, which was delayed for multiple reasons. So this old 1992 Corvette was quickly shoved into the "fast shop car" role, with some planning that began last October.

                          It also didn't make sense (to me) to have both of our shop cars in NASA TT Letter classes - the red BMW E46 330 in TTD and this white C4 Corvette in TTC. That's a little nuts. So back when we were looking at a TTD build for a BMW E46 coupe, we had already decided to move the Corvette out of TTC, or at least test some "big tire theories", with a wheel and tire upgrade to the C4 early in 2016.

                          I suck at keeping surprises, and not sharing pictures of these wheels when they arrived and were initially tested was killing me. Just the 335 Hoosier tires were mocked up on the front (above) a few months back, but I couldn't share that either. These were some new A7s I had sitting around, winnings from the TT3 Mustang. We have half a dozen sets of scrubs, too.

                          continued below
                          Last edited by Fair!; 01-25-2016, 05:49 PM.
                          Terry Fair -
                          2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                          EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                          • #28
                            Re: Vorshlag Budget TT Build: Project DANGER ZONE

                            continued from above

                            While we started out thinking about just an 18x11" wheel and 315 tire (which would have fit under the stock fenders), the 335s fit so well under the stock fenders we measured the car for 18x12" wheels at both ends and pulled the trigger. 18x11 and 18x12 wheels cost the same, and I didn't have any (free) 315 tires laying around. So the 335/345 tire combo was chosen for... budget reasons??

                            The easiest way to add a lot of performance to this TTC Corvette, since we had just had the engine rebuilt to painfully stock spec's, was adding mechanical grip. The easiest path I could think of was to add giant wheels and tires and dump some weight. So I started to do some TT1/2/3 calcs for this car late last season and it looked like TT2 would be a good goal. Here are our TT2 goals...
                            • Goal Weight: 2850 empty, 3050 with driver
                            • Goal P-to-W: 8.0 to 1 (TT2)
                            • Goal power: 381 whp

                            So the 381 whp power goal? Yea, we're not close to that yet, and I will show our dyno tests below with the new motor. We have some things in mind but we figured it was worth testing this theory with the existing ~295 whp power level before we do any mods that could not be "undone", so we had a path back to TTC in mind if the first 2 events in 2016 were a total bust on the big tires.

                            This 2923 pound weight was with the full cage, 18x12" wheels, and half a tank of fuel. The car is still about 75 pounds too heavy

                            The TT2 class move was the reason for trying to lower the weight goal - and why we pushed ahead with the plexiglass rear hatch and snatched out the ballast box and multiple 45 pound weight plates. We still have some pounds to go on this 2850 pound goal (without driver), but there are plans to get there. I was just hoping we could get closer to this weight for the first event, and since we got the car down to 2840 pounds back with the 4-point roll bar, small wheels, and no rear hatch before.

                            If you have read my build threads over the years you know I like to use the biggest wheels and tires that can fit a car, for both road course or autocross use. One of the things our shop is known for is pushing the limits of wheel width under stock fenders on a number of cars: BMW E36, E46, E90, & 1M; EVO X, Subaru GR, S197 Mustang, C5 Corvette, and more. And now we can add C4 Corvette to that list. And maybe.... "fit" is a stretch here, I'll admit. But this car will get some flares soon to make it all look right and cut down on aero drag. We did learn what it takes to stuff a 315 and 18x11" under stock C4 fenders with this test, which is more usable data for most folks' cars.

                            So as you can see the 18x12" front wheel we spec'd "fits" up front with no mods using the 335/30/18 Hoosier. This could work with zero mods for a street car with 11" wide wheels and a 315/30/18, but we wanted to go for broke so I decided on a 12" wide wheel and 335 tire up front. Again, we had so many sets of 335s and 345s from before. This worked so well up front on a 3600 pound TT3 Mustang that I figured it would work as well or better on a 2850 pound TT2 Corvette.

                            The rear has an even bigger tire, the massive 345/35/18 Hoosier A7, used on an identical 18x12" wheel as the front. Yes, this tire should used a wider wheel, like a 13" or even 14" wide wheel. But the CF5 and F14 wheels from Forgestar top out at 12" widths in their 1-piece wheels. We wanted a less expensive set ($360/each) of wheels for this initial "big tire test", so we went with the same widths we used on the TT3 Mustang (18x12" front and rear). As you can see in the image above, the 18x12" wheel works with the 345 Hoosier... but it does have a hint of a squeeze. This is a 13.8" wide tire.

                            This was the fun "lets bolt the front on" test, before we had the wheels powder coated. Just one front 335 tire, tested quick, looked good. Dismount, take to the powder coater, and wait 6 days... Always waiting.

                            FIRST DYNO TUNE + MORE OPTISPARK WOES

                            Back on January 14th, the crew here at Vorshlag had finally installed the rebuilt wiring harness (after 3 days of chasing down "changes") and the engine would crank and run... for 2 seconds. The folks who sold us the "1995 Corvette ECM" were supposed to turn off the security system in the computer (VATS), since our 1992 Corvette's key would be coded differently than the used ECM they sent us. They charged us a pretty penny ($315) for a used ECM, but part of that was "installing your VIN # and turning off VATS", and they were one of only a handful of shops that said they had a manual trans 1995 Corvette ECM in stock, too.

                            Well of course that was bull. It was not in fact a Corvette ECM, but instead a 1994-95 Caprice or Camaro LT1 ECM, made for an automatic transmission. And they left the VATS system on, which was why the car won't run more than 2 seconds. But luckily the guys at True Street Motorsports know LT1s and using LT1edit they were able to convert the ECM to a 1995 Corvette manual trans unit with a reflash. They also reset the speedometer to work with the 345 tire we were going to use (not on the car at this point).

                            The True Street guys fought with the ALDL port (the OBD port) for 5+ hours, calling the new wiring harness supplier (who I will never use again) and attempted some trouble shooting - since this port now didn't work. It worked before with the 1992 harness, but the $1000 custom built, 1992-to-1995 engine conversion harness they supplied seemed to have nothing but problems.

                            True Street had to overnight the LT1 "bench harness" for this style ECM, and remove the 1995 ECM from the car for each tuning iteration. With no ALDL port they couldn't data log during a tune, either, which made it even more difficult. The Corvette was stuck at their shop for 2 days and my tuning bill reflected the added work they spent chasing the harness problems. Oh well, live and learn... next time I'll use my standard "stand alone" wiring harness supplier and just punk on the factory gauges. We still lost the factory oil temp connection with this new harness, which is something I really wanted to be able to monitor.

                            Once the ECM was reflashed well enough where they could make a pull on the dyno, the ignition was apparently breaking up above 4500 rpm. You can see the jagged red dyno curve above, which is with the refreshed LT1 and 1995 ECM + MAF. This curve was beating the old stock LT1 and 1992 ECM tune (in blue) by 25 ft-lbs all the way to 4000 rpms, then it started to tank, then the curve went berserk at 4500.

                            Both of those dyno graphs are uncorrected, and the "301 whp" line was actually the "284 whp", once SAE corrected. Which is the tune we ran at the 2 NASA events last year. The newly refreshed but still painfully stock LT1 engine was pulling strong in the lower revs, but something wasn't right up top. Over 4500 rpms it wouldn't run. By this time it was nearly 2 pm on Friday, the day before the MSR event. I had to take it like it was, hope it was just an Optispark or spark plug problem, and see if we could fix it back at Vorshlag. I loaded up the car quickly and blasted back to the shop. We hadn't even fit the rear wheels yet and we had another car (BMW E46) to finish, too. Rough, nerve wracking day.

                            As I raced back to the shop with the trailer full of Corvette, and I called our shop manager Brad and had him order spark plugs and water pump gaskets to be there in a few minutes. We unloaded the car and immediately started yanking the brand new OEM style Optispark, which was installed back in October when we were chasing the bad 1992 ECM problem. It was a vented, name brand, brand new unit with 0 miles on it. How could it be bad??

                            Ryan swapped the nearly brand new spark plugs for a fresh set of NGK V-power plugs, and I had hoped one of the old plugs had a visibly broken tip or insulator (which would explain the dyno issue). Nope. The MSD billet Optispark distributor was pulled off in October, but it wasn't the problem, so now it went back on. Ryan and Brad thrashed with this while Olof and I worked on cutting the rear fenders to clear the 345s (see below) and Jon and Steve finished up the BMW 330 prep. It was an "all hands on deck" kind of afternoon.

                            The old MSD unit went in, the water pump went back on, the cooling system was refilled with distilled water and a splash of Redline water wetter, the engine was run, and the cooling system burped. Moments later we were cutting the front fenders and by 7 pm the car was loaded into the trailer. Fingers were crossed - there was no way to "feel" the ignition flutter until it was in 3rd or 4th gear, and it was pitch dark outside. I was not going to go blasting down the road with no lights to test this. We'd have to see if the MSD Opti fixed the 4500+ rpm issue the next day on track at MSR... if it didn't rain. Or snow. The weather was beautiful on this Friday, but predictions of COLD, wind, snow and rain were in the forecast for the next day. Yay. And MSR-Houston NASA event was the next weekend, 5 hours away... we needed to test the engine right NOW.

                            MAKING THE WHEELS AND TIRES ACTUALLY FIT

                            While the Optispark was going in, after the car returned from True Street on Friday, all four of the 18x12" wheels and a scrub set of 335F/345R tires were fitted to the C4. The fronts looked a little close to the hood for bump travel and the rears poked out a mile. Time to cut some fiberglass.

                            Making the rears fit took a bit of fiberglass removal. First we laid down some green painters tape then I marked an "eyebrow cut" line, to give the rear some bump travel. At this point the tires stuck out about 1/2" but we would later see that we needed more like an inch of poke. Again, this is an identical 18x12" wheel as the front, and we planned up front to use a bit of spacer to make it fit out back. Long term, these 18x12's might all become front wheels, then we'll get the new M14.2 Forgestar 2-piece wheels out back in 18x13".

                            Fiberglass dust is nasty stuff so we had Brad cutting and me or Olof with the vacuum sucking up the dust, and dust masks. Below right is the initial fit, then I went back with a 2" sanding disc and cleaned up the wheel arch a bit.

                            The front wheel openings were also trimmed, very quickly. There was another "eyebrow cut" at the hood-to-wheel arch portion, just above the tire, to allow for bump travel. This happened right after an Optispark change was finished.

                            That's how it was loaded into the trailer at 7 pm Friday night. Yes, this looks a bit janky, but there was no time to make flares. We really just wanted to test this big wheel/tire combo on track to see if there was a prayer of TT2 competitiveness for later in the 2016 season.

                            SCCA CLUB TRIALS AT MSR CRESSON, JAN 16, 2016

                            I'm going to try to do this event coverage quickly, as it was only a 1 day event and we were just there to test the Corvette and BMW. I didn't really care how we finished, as this was really just an HPDE day that they were calling a "Club Trial" competition event. They had transponders but there weren't any classes, so they used a PAX factor to post "competition" times. Yes, an autocross PAX applied to road course times. I can't make this stuff up.

                            Anyway, we got there at 6 am, an hour before sunrise, and were working in the dark to have both cars ready before a 7 am driver's meeting. The C4 was unloaded, Amy and I did the wheel swap on her BMW, the AIM Solo lap timers were mounted, and we checked everything else we could under pitch black skies. The driver's meeting took a bit and after we got out, right as the sun was coming up, we greeted Brad and Olof from Vorshlag who had come to help. This became an eventful day of "track side car mods" so their assistance was most welcome.

                            The SCCA Club Racers had 25 entries spread across 5 run groups and Club Trials had 30 entries jammed into 1 run group. This is a 1.7 mile course and 30 cars spread out across a VAST array of skill and prep levels makes for a crowded track, but again - this was just a test for both cars.

                            They gridded the C4 in P1 and stuck Amy about a 1/4 of the way down the order. We went out into the first session and it was COLD with 40 degree temps and 20 mph winds all day. I could hear all sorts of tire rub on the out lap so I got the heck out of the way and dove into the pits before I held anyone up. But more importantly, I was able to test out 3rd and 4th gear under load. NO MORE OPTISPARK ISSUE! Engine ran strong all the way to 6000, so that's already a win. But getting no laps meant I'd be stuck at the back of the pack, which sucked.

                            Amy drove the whole session in the BMW with the rear tires rubbing the rear fenders badly, sending up plumes of tire smoke. Did she stop? No, the ran the whole session. Oh well, if she ruins her tires its her own fault. The Bilstein PSS coilovers were sprung too softly and allowed a TON of body roll, so we'd be doing a big spring rate upgrade immediately after this event.

                            continued below
                            Terry Fair -
                            2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                            EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                            • #29
                              Re: Vorshlag Budget TT Build: Project DANGER ZONE

                              continued from above

                              The fix for the rear tire rub on the C4 was to add more rear wheel spacer. We had all the spacers in the trailer stacked to make nearly a 1" spacer, which moved the rear wheels outboard enough to rub less on the inner fender sections. See why I wanted the long ARP wheel studs? Getting no lap time for the C4 put me at the back of the grid for session 2, right next to Mark Council's C5. His transponder didn't work so he got no times, either. So the two of us went from P1 and P2 on grid to P29 and P30.

                              Mark's C5's 4th gear synchro let go right in front of me at the beginning of Session 2 (its already getting a C6 Z06 trans installed at our shop), but I went around him and started picking off cars on every straight. The rear was very bouncy - stock shocks aren't made to deal with 345 Hoosier A6 tires! - but I could drive around it. We're going to need to massively increase rear spring rate and put some real shocks on this car if we keep the big tire setup.

                              So there were lots of spins and traffic in session 2, and I spent the entire time passing slower traffic, but I did manage to get a quick enough time (1:27.9) to move me to P8 on grid for session 3. The C4 also made 5 laps - in a row - which I haven't ever done in this car. This is already a successful test.

                              In session 3 the C4 was passing cars pretty quickly and I managed to lap some other folks 2-3 times in this session. The weather was holding so far (no rain yet) but it was still bitterly cold. Amy's 330 had gone through two different fender rolling jobs in the pits by now, which was a giant PITA.

                              Track side fender rolling sucks - this should always be done in the shop! - but parts delays & C4 prep ruined our schedule on the E46

                              I found a new issue at the end of session 3 - the brakes went away after 6 laps. There was NO pedal at all. WTF? I wasn't even pushing the brakes that hard, and we had added the brake cooling up front. Fresh XP20 Carbotech pads, new Centric 13" rotors and Motul 660 fluid should have lasted longer than that. The cornering speeds were way up on the big tires, so I was going down the straights faster, but nothing like we did in the TT3 Mustang (this C4 feels like it has less than 300 whp - come to find out later, it does). You can see this at the end of the 4 minute video, linked below.

                              After I lost the brakes I dove into the pits, limped it through paddock and barely got it stopped in front of our trailer after pumping the brakes many times. Brad and I bled the brakes, which already had Motul RBF660 and almost no laps on the fluid. A little air in the right rear but a LOT in the left front (that's a clue). The new front brake calipers had less than 10 total laps on them. The AP caliper temp indicator strips didn't show much heat in any of the calipers, but the left front was a tick higher at 370°F (the other 3 calipers barely registered on the strips). That temp shouldn't boil Motul 660? Maybe the fluid had been in there so long it had absorbed water? Oh well, it was fresh after a full system bleed.

                              With a quick time I was gridded P1 in session 4, but it started to rain before we went out. Oh great, giant slick tires and I don't even know if the wipers work! I was going to just make some laps in the wet and test the brakes again. I let the C5 Corvette gridded P2 go around me at the start, as the old Hoosiers take a lap or two to get up to temp, but I reeled that car in and we both caught the back of the field at the end of the first hot lap. Like I said, big discrepancies in lap times in this large 30 car field, spread out on the short 1.7 mi course.

                              After a number of passes I got little bursts of clear track, and the rain wasn't much more than a sprinkle. I was gaining confidence in this janky test setup more and more, taking corners faster, braking less and less for the high speed sweepers like Big Bend and Ricochet. I was almost feeling like I could take come of these fast corners with the throttle matted.... almost.

                              Again, after 7 laps of mostly traffic, the brakes went away abruptly. No hints, not softness creeping into the pedal, instantly gone. Just nothing there. At all. Luckily I was held up behind a BMW for most of a lap and had backed off to about 50%, trying to build a gap. When I sped up to take lap 8 at speed, going into Big Bend, I went to touch the brakes... FLOOR! Nothing. Well luckily there was some "grip reserve" and I was able to take Big Bend without any braking whatsoever, hehe.

                              I dove into Pit In, downshifted a few times to slow down, then crawled to the paddock in 1st gear. I pumped the brakes furiously, nothing. Had to shut off the motor with the car in gear in the pits to get the car to stop, or else run into the back of the trailer. Yikes. Glad I did that session to test the freshly bled brakes, since this is not the fluid boiling. Something else is going wrong. We let the car cool off, winched the Corvette into the trailer, swapped wheels for Amy's BMW so she could drive it home, and got out of there before the rain got any worse.

                              Raw time results from session 3 (dry) and session 4 (wet). DangerZone was quickest of the day?

                              The C4 was once again fastest in "moist" session 4, and only a 1/2 second off my dry session 3 times. Again, I was still learning the car and this new "big tire setup". The 1:23 lap times aren't all that impressive on their own, as we've run 1:17s in the TT3 Mustang here - but we did that in much warmer weather. This January weather was brutally cold and the other racers were commenting that their times were 2-3 seconds off the mark. Whatever, don't care much about lap times this day - this was still a productive test for both cars and we learned a lot.

                              I came away from this test feeling... cautiously optimistic? Some of the folks here would be at the NASA TT event the following weekend, so I could compare to them there. This was the first time to really put laps on the new springs and rebuilt shocks - the front felt pretty planted (1170 #/in custom transverse spring by VBP) but the rear didn't feel good at all (510 #/in stock '84 Corvette Z51 rear spring). There was a lot of rear suspension "wallowing" that had me a bit concerned. MSR-Cresson is notoriously VERY SMOOTH and the back still felt unsettled. How would this work at MSR-Houston, which is much bumpier in sections? Could the rebuilt but still stock dampers handle the added grip from the 345mm A6 tires? Are the 25 year old, rotted rubber suspension bushings going to bite us now with the bigger grip? We would see in a week...


                              We unloaded the C4 on Monday morning and took a closer look at the caliper temp strips and the tire rub evidence. Wow, the rears really self-clearanced the fender liners. The most damage was done on the very first lap in session 1, where the inside rear sidewall on the right rear dug into a suspension bracket (see below), which cut a groove into the edge of the tread. This initial rubbing was why we added more spacer and swapped the rear tires side to side. We kept an eye on this tire all day at MSR-Cresson - the groove never worsened - but this tire will still be thrown away and never used again.

                              The calipers barely even registered any heat at all, so the brake cooling wasn't the issue. Ryan and Brad tried to re-bleed the brakes but it never got better - car had "no pedal". This meant we had a bad master cylinder. I made some calls and the previous owner of this C4 (Matteucci) mentioned that he had replaced the master cylinder once already (installing a reman 96 model). We also noted that another C4 customer in the past had gone through 2 or 3 masters as well. Its back to "old car problems" again - a freshly rebuilt master cylinder for a 1996 model (which ensures we get one valved for the 13" front brakes) was ordered.

                              We also scheduled a dyno pull at True Street, to get the legal pair of SAE corrected dyno pulls for TT1/TT2 classing. I thought briefly about running TT3, where this car should really be classed (for it's P-to-W and lack of aero), but we wanted to hopefully stay in the same class for the entire year for this car, and I really wanted to add aero and more power now that the "big tire test" seemed to be successful. And why run TT3 again, when we had already run that class successfully for 3 years in the Mustang?

                              True Street squeezed us in Tuesday morning (1/19/16) so we loaded up the C4 (with non-functional brakes) Monday night and I took the car there first thing on the morning of the 19th. The C4 was strapped down with the correct sized tires (first dyno test on the 345 Hoosiers, which will sap a little more power than the 245s) and after the engine was warmed up Sean made two dyno pulls in 4th gear on their DynoJet in-ground chassis dyno. Temps were in the low 40°F range, so there were bigger than normal correction factors.

                              The best it made was 296 whp and 363 wtq, using the common STD corrections. That translated to 288 whp/354 wtq with the SAE correction factor that NASA wants to see. Hmm, we've got a long way to go to make 380 whp for TT2, but that is a battle for another day. The dyno curve was smooth and looked remarkably similar to the bone stock 284 whp dyno curve done in January of 2015, but there's a solid 20-25 wtq bump from the bottom to around 4000 rpm, then the new motor seems to choke out and make nearly the same peak power number as before (284 whp then vs 287 whp now, both SAE).

                              Of course there's a restriction somewhere - either the anemic 1992 LT1 camshaft, the stock throttle body, the smallish MAF sensor, the stock catalysts, or the stock exhaust manifolds are choking the life out of this engine, but 296 whp is pretty normal for a stock LT1 with a super light flywheel. Remember, this car's 7.25" multi-disc clutch/pp/flywheel is a solid 50 pounds lighter than stock, which all translates to more engine acceleration, which adds power on a dyno - even if its kind of fake.

                              ARH makes C4 headers in 1-3/4" and stepped 1-3/4" to 1-7/8" primary long tubes, with an X-merge, with and without cats

                              For TT1/2/3 we can do damn near anything we want to add more power - heads & cam, crazy exhaust mods, an LS1 swap, turbos, you name it - but we'll look at a long tube header & freer flowing exhaust upgrade first, then see where we are on the dyno. The ARH long tubes for the C4 (see above) should add 30 whp by themselves, if not more. We'll ditch the 25 year old catalysts and the choked up after-cat system, which should add another 10-15 whp. So look for power upgrades to be added and tested throughout the 2016 season, if things work out with DangerZone in TT2.

                              After the two quick dyno pulls I loaded the car back up and got it back to the Vorshlag shop. Ryan quickly installed a new 1996 master cylinder and - viola! - the brake pedal is back. He also checked the car stem to stern for a pre-track inspection - nut and bolting everything, fixing some fender structure that had worn through, etc. They did an oil and filter change, going from dyno based high zinc "break-in" oil for the new engine, to 15W50 Mobil1 synthetic for the next 2 race weekends.

                              The crew also fabricated the rear tow hook, shown above. This bolts to the rear aluminum crash beam, which is pretty beefy - we should lighten that the next time the rear bumper cover is off (bumper cover is a total MOFO to remove - takes 2-3 hours, with small hands). This rear hook has a 2" inner ring, which is the required size by NASA and SCCA. Just nice to know its back there, if I nose this thing into the weeds and need a tow. Hopefully it will never be used.

                              The past 25+ years haven't been kind to the front air dam plastics, which were falling off and damaged when we got the car. One piece was held on with about 6 pounds of Gorilla Glue! The low ride height and shorter 245/40/17 tires we ran last year made this worse. Now that the car is sitting up a bit higher on the taller 335/345 tires it was time to swap on the new GM plastic pieces. Ryan had to reconstruct much of the support structure on the left (and scrape off the Gorilla snot) but he got them all on and aligned correctly. These pieces help force air into the "bottom feeder" radiator air intake, plus keeps some air from going underneath the car (reducing lift).

                              WHAT'S NEXT?

                              I was going to wait and include the write-up for the upcoming NASA event at MSR-Houston in this update, but it is already running long, so we'll cut it off here. Here is the first third of the NASA Texas 2016 schedule:
                              • January 17-18 – MSR-Houston, Clockwise
                              • March 14-15 – MSR-Cresson (the 1.7 if we have less than 34 cars in TT, or the 3.1 if we have more)
                              • April 25-26 – TWS

                              Obviously we're taking the C4 in TT2 (and the E46 in TTD) to this weekend's NASA event. The TT2 competition signed up already looks brutal - 10 registered in class, including several Z06 Corvettes, a Porsche GT3, a race prepped EVO, and more. So yea, DangerZone might not pose much danger to the class right now. We're under powered for TT2 by about 100 whp, the rear spring rates are all wrong, and the shocks are laughably inappropriate for these tires.

                              So this first NASA event at MSR-Houston will be a "let's just get points" opportunity and more shake-down runs for this new "big tire" setup. I'm not even going to burn the set of Sticker tires here, since we'll be pretty far off the TT2 pace. Amy has one other TTD competitor so I'll try to help her do her best, but that car is also under-prepped for the class at this point. First event of the year - we both need a lot of luck to score points here, which might help us later in the season.

                              Until next time,
                              Terry Fair -
                              2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                              EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                              • #30
                                Re: Vorshlag Budget TT Build: Project DANGER ZONE

                                Project Update for March 25, 2016: When we last left off the C4 had been raced once at MSR-Cresson and set FTD for the SCCA Club Trials. There were some issues with the brakes, and the shocks didn't deal with the minor bumps at Cresson, both of which gave me pause... but I ignored that and pushed forward on the "Big Tire" TT2 plan. We did some quick fixes to the brakes, then went to with NASA at MSR-Houston, one week later. After that we had a little time, so we made some changes and ran another event with NASA in March, back at MSR-Cresson again. We played a bit of "musical chairs" this time, but I will explain the what, why and how below.

                                MORE JANUARY PREP WORK

                                My last forum build thread post ran long and I left a few things out due to space. While I was writing the last few bits of that post, a few extra changes were being added before the January MSR-H NASA event, which I will go back and show below.

                                For the first "Big Tire" test at MSR-Cresson we had stacked up a bunch of smaller spacers on the rear wheels. We had spec'd these custom 18x12" wheels to actually fit the front with a 335mm tire, hoping that in the near future we would buy some wider 3-piece rear wheels (18x13"?) for the massive 13.8" wide 345/35/18 Hoosiers. If that happened then all four 18x12's we built the same way could become front wheels, leaving us with two full sets of race wheels again. Its always smart to have a full back up set of matching race wheels, so you can practice on your "old scrubs" and save the sticker set of tires for that "golden session" of the weekend.

                                To make these "fronts" fit out back for now we just used a couple of small spacers. During this January SCCA Club Trials event they rubbed inboard with the 345s, especially in hard corners, so we kept stacking more spacers out back until the rubbing stopped. The result was we were left with a LOT of tire poke at the rear (which I detest), but we were going to cover all this with custom built flares later, so I wasn't too worried. As long as the car still fit inside the trailer (it did, easily) it wasn't too wide. More track width adds mechanical grip, and since this wasn't an autocross car, the added width wasn't going to "kill the slaloms".

                                After this event, back at our shop I removed a rear wheel and measured "the stack" of spacers. I took this measurement and found 1-piece hub-centric spacer for use at the next event. This would be safer and less janky than a bunch of mis-matched spacers stacked up. I found .875" thick aluminum spacers from Bear Racing - the pair is shown above on the scale. These 1-piece spacers fit the hub bore and bolt circle of the C4 perfectly. I'll talk about how these were re-purposed later in this thread...

                                I forgot to show in my last post where Jon was adding new graphics for the move to TT2, as well as a few other new decals for Forgestar and the "Rampage" rear license plate. These are made on our 24" wide vinyl plotter, shown at right. Nothing fancy but it works well enough for simple graphics for our shop cars and a few customer cars we maintain at the shop.

                                Another thing that I had always meant to do to this car, even when it was in TTC (we had taken points for it), was open up the factory LT1 "air box". As you can see above, the intake manifold is fed by a rubber tube (now with a MAF sensor added) from an air filter "enclosure", or air box as we like to call it. By the way, there is no direct path for air to get into this semi-sealed area ahead of the radiator inlet duct. Air just bleeds around and through gaps in the bodywork to feed this area. We can (and eventually will) add a "ram air" inlet on the front of the car (front license plate pocket lines right up) to feed the air box with a good high pressure source of fresh air. For now I just wanted to open up the factory air inlet hole and remove the air baffle on the front of the air box.

                                Above at left is the unmodified factory airbox, which holds a pleated paper air filter and has a baffle on front - to cut down on noise and to keep the filter from getting wet. The "quietness" of this car doesn't matter to us now, nor does a little moisture from running in the wet (we don't even have real "wet" race tires, so if rain is falling this car isn't likely running). Getting more air into this choked up airbox was the goal. In stock form all of the air flows in through a single rectangular hole, after it travels through a plastic air baffle - which is shown above at right, already removed.

                                The real fabricators in our shop were busy on billable customer work so I hacked up the airbox myself, after we were closed one day. First thing I did was drill out the rivet heads to remove the air baffle. Then I scribed out two new rectangular openings on each side of the factory hole. This was done quick and dirty, with just a few measurements and a straight edge. I marked, center punched, then drilled some holes in each corner to make the new openings have rounded corners, to try to match the OEM hole. Then I used a small jig saw to join the drilled holes. End result was two new rectangular openings with rounded corners.

                                For being 25 years old the air box was in great shape. After the 2 new openings were cut, and the edges deburred and sanded smooth, it was ready to prep for paint. I scuffed the painted metal with some Scotch Brite pads and cleaned everything with wax and grease remover. Once that dried it was hit with 3 light coats of black paint.

                                This is the final result, above. I may have rushed the drying of the cleaning solvent, as the paint fish-eyed in some sports. Oh well, its hard to even see this air box with the clam shell hood up. More importantly - the baffle was gone and the surface area of the opening in the airbox more than tripled.

                                We looked at some aftermarket "cold air" kits for the LT1 C4 and the few choices still available were not very appealing. Sure, we should add a more direct path of fresh air from the front bumper to this now opened up enclosure, but for now it was a $3 upgrade (cost of paint) that was well worth the hour it took me to do. There is indeed more intake noise, so maybe there would be a tick more power on hand for the MSR-Houston event? I'd be running nearly 100 whp down on what a real TT2 car at this weight should be, so anything would help.

                                One last little update. After the January SCCA Club Trials, when the brakes failed in two sessions, we replaced the brake master cylinder with another reman unit (we cannot find new master cylinders for this car). This might be the 3rd or 4th reman'd MC this car has seen, but when it was installed and bled the pedal pressure felt right once again. Let's see how long this one lasts? As with all track cars we build, the cap to the plastic fluid reservoir got wrapped with a shop towel and zip tie, which usually soaks up the small amount of fluid that might puke past the cap under high temps. The original vacuum assist brake booster is still on the car - and its a PLASTIC unit that is a known failure point. More on that in a bit.

                                NASA AT MSR-HOUSTON (CW) JAN 23-24, 2016

                                The MSR-Houston track is not nearly as smooth as MSR-C, but that thought never entered my mind before we got here. Why? I've always raced cars here with GOOD monotube adjustable coilovers, so it never felt bumpy in the 7-8 times I'd raced here before. Boy was I in for a surprise in #DangerZone!

                                We took both the Corvette and BMW to this 2016 NASA season opener event at MSR-Houston. We loaded up Friday morning and slogged through 6.5 hours of driving, most of which was burned inside the city limits of Houston dealing with their nightmarish traffic (normally this is a 4 hour drive from Dallas). I was towing our enclosed trailer with the Corvette inside and Amy drove the TTD classed BMW 330 down.

                                When we arrived it was pitch dark and the paddock was packed. We got lucky and found a wedge shaped spot close to grid where we unhooked the trailer and parked the BMW. Amy had Tech inspect the BMW for Annual TT Tech and a new Logbook.

                                It was too dark and too late to extract the Corvette and make the close of tech that night, so we got to the track early Saturday morning to take it through annual tech before the first TT session. Well, in the rush we did not put the safety wire into the Schroth harness clips in the C4. Without it, we could not pass tech. I pulled out of line, went back to paddock and added the safety wire to "lock" the clip-in latches closed. I got back in line to re-tech but the TT field had already gone out on track. I got my tech sticker, drove straight to grid, belted up and went out on track.

                                They threw the checker as I came around on my warm up lap so I didn't get a time. This meant I'd be starting from the back of the grid, which makes for an extra challenge. I was also trying to drive BOTH of our TT cars both days, so I had my hands full.

                                This was the debut NASA event for our BMW E46, which we had planned on running in TTD for 2016. We're doing a "build progression", with parts being added along a set build plan, hopefully showing incremental improvements along the way and testing products we make or want to offer. So at this event the BMW was PAINFULLY under prepped (150 pounds over weight + 50 whp down). Unfortunately, the Corvette was also very under-prepped for TT2.

                                We had a little bit of a break after the first "warm-up" TT session, which is only used to get times for the gridding of cars in the first "official" TT session. So I had no time in the TT2 Corvette and gridded at the back in this next session. I went out on track hoping to get the tires up to temp by lap 2 or 3. That ended up never being an issue - even when "cold" these massive A6 Hoosiers make MONSTER GRIP. Lots of people think that if a tire isn't at its peak temperature that it will have zero grip. That was NOT THE CASE in this car... it made TOO MUCH grip from the very start.

                                Event Photo Gallery:

                                The massive mechanical grip plus the bumpiness of this course added up to one of the scariest laps Ive driven in my 29 years of experience with track events. There is a straight section of this course between T14 and T13, right before the hill you almost jump they call "the launch", which was especially bumpy. I had to back off a lot here just to stay on the track. I have never noticed the bumpiness there in any previous car I've driven at this course, or in our BMW this same day, all of which had been on proper shocks. Driving this track in the C4 was a "life altering experience". After a couple of laps and almost skidding off the track going in a straight line I pulled into the grid, white as a ghost.

                                That. Was. Not. Fun.

                                I realized, right then and there, that this Big Tire test was a terrible idea without buying real dampers and changing some other components. Adding 100mm of tire, and going from an R7 to an A6 compound, showed the true limits of the 25 year old Delco Bilsteins. I had run this track the year before in this same car on the little 245s to the tune of 1:43.7 without any handling drama... this day on 335/345mm tires I could barely manage a 1:48.9 with a fresh motor and many other upgrades.

                                continued below
                                Last edited by Fair!; 03-25-2016, 08:55 AM.
                                Terry Fair -
                                2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                                EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev