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Unread 01-25-2016, 03:46 PM
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Default 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 370F (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...

ANOTHER DYNO TEST + NEW MASTER CYLINDER + REAR TOW HOOK

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 40F 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,
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