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Vorshlag C5 Corvette Development Thread

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  • Fair!
    started a topic Vorshlag C5 Corvette Development Thread

    Vorshlag C5 Corvette Development Thread

    Project Introduction - April 10, 2014: This was originally a build thread for a customer's C5 Corvette, Mark Council, which morphed into a C5 Development Thread. I normally I won't make a "Vorshlag Build Thread" for every customer's car we work on, but this one is a bit special. Mark is testing out some new things we're either making, sourcing, or selling. On top of that he let me race his C5 at Optima already and I will likely take laps in testing in the future.

    Picture above is from an autocross in August 2016

    This 2002 Z51 6-speed Corvette was being built as a "track rat" that (for the moment) can still be driven to a road course, but with few other considerations (and he's already truck / trailer shopping, so that requirement may go away soon). It later turned into an autocross only build. Initially Mark was just looking at getting some wheels and a few things repaired, but his car came to our shop at a time when I needed a car to drive at Optima... so we worked out a deal and this C5 became a bit of a test bed for us to try some new parts.

    We met Mark at the May 2013 NASA event at NOLA Motorsports Park, where he was autocrossing with the local SCCA

    I met Mark in May of 2013 at NOLA Motorsports Park (above) when we were racing with NASA down there. It was a crazy weekend, my first time to run that track in anger and ended up being one of my strongest finishes of the year, obliterating the TT3 record and outpacing all but one TT car that weekend. Mark was there to autocross with the local SCCA region and convinced me to come do some fun runs with them on one of the dedicated autocross pads at NOLA. It was only about 200 feet from our paddock spot, and Mark rode though to navigate and show me the course - where we set the fastest autox time of day in our TT3 road course set-up with zero changes, heh. Crazy weekend where all the stars aligned.

    Mark's 2012 Mustang has been modified for autocross and track events, but he wanted more than this chassis could deliver

    Mark had already purchased some 18x10" race wheels and some other bits from us, but after that NOLA event he worked more closely with us to get more parts and work done at our shop to his 2012 GT that transformed it from daily driven commuter to a real autocross and track terror. He took it pretty far down the autocross path, then realized... it was always going to be a stick axle Mustang. What's better than even a great set-up S197 pony car? A Corvette! Well... maybe we pointed him in that direction, who's to say? He also wanted a "dedicated track car" and is looking at a "dedicated autocross car" using another chassis, which we might build for him also. That thing... well, I can't talk about it yet.

    Here are a couple interior pics of his 2002. Brey-Krause harness bar, Scroth harnesses, Sparco EVO II seats are nice.

    Mark got a great deal on this silver-ish 2002 C5 Corvette "fastback" (non-FRC/non-Z06) in early 2015 that already had some good parts on it (headers, Sparco seats, Schroth harnesses, B-K harness bar) and a few not-so-great parts (Konis, Borla sound amplification unit, very grabby clutch, and a piss-poor engine tune).

    Borla exhaust is going away soon (left) but the engine bay has some nice parts (right) like a Ram Air set-up, full length headers and a cam

    He started a build thread on the Corvette Forums located here and I'm sharing more of the work we do on this Vorshlag Project Build Thread. Our thread is posted and will be updated on these forums:
    Why is the C5 Important?

    The answer is simple: the C5 generation Corvette is probably the best bang-per-buck track car in the world right now. Nothing else can match this car's factory road course performance, suspension, horsepower, brakes, and low aero drag of the C5 considering the used car prices they are selling for right now ($12-25K+). That's a bold statement, I know, but its the truth. And while we've been able to beat most C5s in the same NASA power-to-weight class with our TT3 Mustang, we had to go pretty hard core to do that (345mm Hoosiers, massive aero, high end suspension mods and brutal drives).

    Left: Aluminum subframe and composite springs are unique to the Corvette. Right: Look at the frontal area compared to this S197 Mustang!

    The C5 was a pretty radical departure from the C4 chassis, but they share a lot of the same roots. Very low center of gravity, good front-to-rear bias, composite bodywork, low drag aerodynamics, but also a small-ish cabin that can be a challenge to add a roll cage to or to fit around taller drivers. The GM "Y-body" chassis is a halo car program shares it's chassis with no others (we will ignore the "Cadillac thing" that was based off the C6), and it is very nicely priced when new compared to its peers - the Viper, the 911, and a few others. And like I said, used prices on the C5 and C5 Z06 are astonishingly low right now. But finding a clean, unmolested C5 Z06 is getting more difficult and prices have started to go up a tick. So Mark skipped the Z06 and FRC models for the lower cost, more abundant, and swoopier Fastback Coupe.

    The C5 (1997-2004 model years) moved away from the short-lived Gen II "LT1" family of engines to the all new Gen III "LS1" engine, which was revolutionary in many aspects (and still extremely popular today). The ZF S6-40 6-speed manual of the later C4s was also tossed in favor of the Borg Warner (now Tremec) T56, which was 25 pounds lighter, quieter, and performed as well or better than the ZF. The C5 also was the first Corvette to get a hydroformed steel frame, which was much more rigid than the welded sateel frame on the outgoing C4, and massively cut down on squeaks and rattles. It also got the first Corvette rear transaxle, where the transmission and differential are housed behind the driver. This improved weight bias to 50/50. It also is unique in that it came in 3 distinct body styles: fastback, fixed roof coupe and convertible. A total of 248,715 C5 Corvettes were built from 1997-2004, so there are plenty out there to choose from.

    The "Fixed Roof Coupe" C5 (at left) may be a hair lighter, but the "fastback" Coupe (right) has cleaner aero at speed

    This C5 "fastback" body shape is advantageous over the FRC/Z06 trunk shape at higher speeds, so that's a plus. The prices on good Z06s have gone UP lately and the best parts of a Z06 would be replaced on a build like this anyway (cam, intake, exhaust, springs). It is actually a bit harder to find a fastback with a 6-speed manual, but there are cost advantages when you do find them, and the weight differences are almost a wash. The lightest I've ever weighed a stock C5 Z06 was 3048 pounds with zero fuel (and the OEM titanium exhaust) and this one came in at 3114 pounds with 1/4 tank. So its... about 40 pounds heavier? That's not a lot. The C6 was 3150-3300 while the C7 has ballooned up to 3400-3500 pounds (depending on model and options). The 2011-14 Mustang that Mark is leaving was 3600 pounds in stock form and the latest IRS S550 chassis Mustang is 3750-3800!

    And while Vorshlag isn't "known" for Corvettes, we have worked on quite a few, and I personally owned and raced several C4-C6 Corvettes (see above) in my early Vorshlag days. I respect this chassis immensely, and my only hang-up with the C4/5/6/7 chassis in the past was that they handled SO well out of the box, it was hard to make them a LOT better than stock (not like we can do with McStrut cars). But after driving Mark's C5 car in the Optima 2 day competition, I noticed it is in fact easy to make them handle WORSE than stock with the wrong parts, heh.

    Not to mention we have gotten pretty far ahead of the "stock handling" and road course performance with our NASA TTC/PTC classed, 1992 C4 Corvette (Project #DANGERZONE, shown above) that I am racing this year, and a lot of the same principles can be applied to this C5. Upping the spring rates in the right proportions, install better dampers, change out rubber bushings, lower ride height/CG, add power, and add wheel and tire width. Plus improve brake pads, brake fluid and brake cooling. Then develop some downforce with it, using the right techniques and parts. So yea, maybe we can make a C5 significantly better?

    More tire, more downforce, more spring, more damper.... its a proven formula, if you know what parts to use or how to build them

    And that's pretty much what we have planned for Mark's car. Shocks, spring rate, bushings, wheels/tires, aero, a better engine tune, and a quieter yet higher flowing exhaust. We will use some off-the-shelf parts, some "tweaked" parts, and maybe a few all-new designs. The Corvette aftermarket is pretty crowded, for sure, but there's always room for "a better mouse trap". I don't want to make "me too!" parts, something just to mimic everyone else's existing upgrade options, and if someone else makes the best part that we cannot top, we will use that. Otherwise... we have engineers, fabricators and machinists on staff.

    We have the tools.... we have the technology...

    continued below
    Last edited by Fair!; 09-03-2016, 03:55 PM.

  • Fair!
    Re: Vorshlag C5 Corvette Development Thread

    continued from above

    We ate well in the Haymarket district restaurants with a different group of racer friends each night: Buzzard Billy's had decent Cajun food, BurgerFi had a great burger and onion rings, and we had some good grub at Lazlo's.

    I didn't get much sleep that week, however, as a certain somebody who's room I shared snored like an unmuffled rotary at full revs. I stayed up and watched the F1 race, surfed the interwebs, and listened to music on my phone until there was a break in the sound, then I would doze off and try to start my side of the snoring battle. With 1-2 hours of sleep each night it began to catch up to me, but I managed to drive "about like I usually do" through mild sleep deprivation.


    Tuesday morning bright and early was already hot - damn hot - and breezy. Sunday, Monday and Tuesday were all sunny days with ambient temps in the 95°F range each day, so I made sure to drink plenty of water and consumed most of a case of Powerade that week. Always with a drink in hand, trying to stay out of the sun, and slathered in SPF50 sun screen when I needed to walk course or stand in grid. I managed NOT to get heat exhaustion or sunburned all week, which was a major accomplishment for me.

    It was super busy that morning, and I was assigned course work during heat one for FP, GS and STX Ladies. The West Course kept us hopping and the 1.5 hours flew by quickly. Then we waited for one heat in our paddock before another course walk between heats 1-2 and we gridded up in heat 2.

    Day 1 run 3, Terry driving terribly

    I didn't bring my good camera with us to grid on Tuesday so all of these pics are from Wednesday on East course. The in-car video above is my 3rd and final run from this West course, which kicked my ass. It was hard to see and I got caught out with mistakes on every run. Mark and I both had trouble here, as did many others - even the designer for the West Course coned every run on his own course.

    I stayed off the cones, but probably too far off. I was driving too conservatively, always seeming to get on throttle too late, turning in too early and getting "behind" on the cones in every section. This made for some slow times, which seems to be par for the course lately for how I've been driving in Mark's Corvette. Which is a shame, because the car was working beautifully! I managed to stay out of "Ice Mode" on the ABS, which seems to be less prevalent in this car on concrete than on asphalt. It is still there, but just harder to achieve.

    There was a 3rd gear shift necessary in the final section before the finish that I struggled with. In my 2nd run I was going for 3rd and hit a bump, which popped my visor halfway down, and the bottom edge went right across my vision. I was blind for about 3 seconds, so I reached up and popped the visor down so I could see, then when I looked up again I was 30 feet offline and about to plow down some cones. My first run was crap and this nearly aborted run matched that time, so I went into run 3 with nothing but junk. It was more of a "safety" run than anything, trying to be clean and salvage something for day 2.

    Mark had issues on every run and his 1st attempt ended up being his fastest. He started off well but just never got faster, which always hurts. I think we were both caught off guard at the higher grip levels available on Rival-S tires on concrete, as neither of us had any experience with this tire on this type of surface. Both the OKC and Texas Region SCCA events are all held on asphalt - we lost our last 2 concrete lots in Dallas 2 years ago - and it shows. We kept trying to push ourselves to go faster, but the tires always seemed to have more in it.

    Serious autocrossers will travel to Lincoln to run the Spring Nationals and even some of their regional events before Nationals, and we should have done that. But Mark was still dabbling in SSM on Hoosiers earlier this year, and I had no intentions of taking anything to Solo Nats, so we just went up more on a dare than anything else.

    CAM classes: CAM-C had 27 drivers, CAM-T had 11, and CAM-S had 21. After the 3 runs were over for day 1 we had both fallen to mid-pack, 11th and 12th out of 21 in CAM-S, and almost 2 seconds out of the lead. That night someone told us that a cone was found for another CAM-S competitor ahead of us, so we moved up to 10th and 11th. Not a good place to be heading into day 2, but I was doing the rain dance and hoping for a miracle - which is what we would need to move up significantly.


    We didn't walk the East Course until the end of the day on Tuesday. I won't walk the 2nd course in a 2-course event until after the 1st course is done, to keep my mind clear. We walked this one again Wednesday morning.

    This course flowed better and was much easier to see. I enjoyed this course better even with the wet and dry conditions.

    I worked course while Mark worked Impound, and the skies looked pretty bad in first heat. The entire heat 3 was CAM cars but we got a few STX drivers to help us work on Day 2, to balance out the worker load. I got paired up on corner with the head of the STAC, who had some great comments about the Street Touring category - which I watch closely and raced in for 5+ years (STU) starting back in 2005. We stayed dry the majority of this heat but it started to sprinkle at the beginning of 3rd runs, and really started to rain in the closing minutes.

    After heat 1 we went back to the trailer to stay dry and the rain came down hard in heat 2. C-Prepared was running and the wet conditions really shook things up. I was hoping for a continuous light rain, to keep course wet but still driveable. It stopped raining about 30 minutes before we needed to head up for heat 3. That's right when my sister called and told me our father had died. This was a huge shock and it messed with my head. A lot. I had to drive in less than an hour so I tried to wrap my brain around driving, visualizing the course, and thinking of ways to catch up some time versus other CAM-S drivers.

    Mike "Junior" Johnson's flared C3 has LSX power, giant Rival-S tires, and weighed in at 2934 pounds. He took 3rd in CAM-S

    The grid area was sopping wet but the rain had stopped as CAM gridded up for heat 3. There were substantial puddles on course, mostly on the right side... which was the start and finish areas. The rest of the course was still wet but the wind and sun were drying things quickly.

    Richard Jung's CAM-S 1968 C3 Corvette also has LSX power and tips the scales at 2950 pounds

    I went out first (I was 99 to Mark's 199) and it was still very wet, but I pushed the car hard trying to set an early quick time. I hit the first cone in the first slalom but had a decent raw time. A number of other driver's had cones on their first wet runs, too, but Mark managed a clean and faster run in the later part of the first runs - he was the last car to take the course for CAM-S each time, being # 199. This moved him right into the trophies, so we had some small hope there.

    Run 2 was getting dry on the left half of the course but still sopping wet on the right. I dropped 3 seconds into the 69.0 range but again, hit the same cone in the first slalom. I wasn't even aware I was hitting it but the cone sheets don't lie. Mark went even quicker with a 66.5 time on his 2nd run, solidifying his trophy position around 5th place now, even better.

    We go into run 3 and I am sitting on cones and I really need a "hero run" - finally clean and much faster. All of the CAM drivers are dropping several seconds per run as the course dried out, and the 2nd drivers are seeing even drier conditions than the 1st. I was the final "1st driver" to take the last run on West course and I gave it all I had. I dropped another 3 seconds to a 64.102 second run, which felt incredible. If the video would have worked for our last runs I would show it... it was precise, faster, and I felt good about it. This run moved me into 5th and final trophy spot as I came across the line, and I gave a hoot and a hollar!

    Mark had the driest look at this course in CAM-S, and he dropped 1.6 seconds to a 64.917. But by then the 2nd driver CAM-S times had dropped into the 63 and even 62 second range, so he fell out of the trophies and down to 11th. At the end of heat 3 my 3rd run was the 6th quickest in class, but I was too far back from day 1 and finished 7th of 21, one spot out of trophies by .277 sec. Here are the Official Results.

    Shawn Lambert and Eric Brown took this 2002 C5 Z06 to 1st and 5th in CAM-S class on BFG's... this tire took 1st-12th in class


    We went back to our paddock spot, a little down but glad that one of us could catch up a few spots. Mark said he was happy with finish in his first ever Solo Nationals, but I'm never happy with anything other than 1st, hehe. We went to lunch as the sun came out, which made the site a humid and wet mess, grabbing some mediocre Mexican food and plenty of water. We had time to kill before the banquet, which was slated from 5:30 until 10 pm.

    After our 2 hour lunch break we came back, loaded up the Corvette and packed the trailer for the drive home Thursday morning. We got cleaned up at the hotel, made it to the banquet hall early, and talked to dozens of folks. Right as the "banquet chicken" lines opened up for the Tues-Wed banquet, we eased our way out of the hall and again went to the Haymarket for Indian food at The Oven, which was amazing. We ran into some Texas Region SCCA folks and shared a table with them.

    Thursday morning we hooked up the F-350 to the trailer and said our goodbyes. Apparently there was a MASSIVE rain storm some time after we left - 2 inches fell in 20 minutes - and some associated controversy over the event stopping, some drivers getting dry runs before/after the rains, etc.

    Texas Region's Feras Qartoumy built this 72 Nova at home, but "don't call it the Murder Nova"

    As I write this at least 5 classes are still under protest or appeal, but eventually that will get that sorted out. I do dislike the "some wet / some dry" runs in the same heat, but its Nebraska in September - IT ALWAYS RAINS.

    Keith Lamming in CAM-C had an unusual thing happen to him on course: airbags exploded. This is a known issue in the 2010-11 5th Gen Camaros, where high grip slaloms will trick the car into thinking it is going to crash and the curtain airbags deploy. Keith said he normally removes the air bag fuse before any autocross run but simply forgot this time and it "did what they all do" in autocross. This isn't a thing on 2012-15 5th gens, apparently.

    Long time Optima racer Todd Rumpke passed away early during the week of Solo Nationals. He was 53 when he lost his battle with cancer last week. There was a big tribute to him at LS Fest this past weekend where Danny Popp drove his C6 Corvette in competition. I remember Todd from when I raced against him at OUSCI. The news hit everyone hard.

    Tony "Rosco" Rietdorf was at Solo Nationals and ran the CAM Challenge in his SN95 Mustang. Sunday night after the Challenge he fell off the back of a golf cart in paddock and his head hit the concrete. An E.R. doc was on the scene within seconds but Tony was unresponsive. The EMTs arrived quickly and he went to the hospital where they induced a coma to reduce brain swelling. There was a GoFundMe page created to help pay for his medical costs, which is still up. We got news last night that he passed away. So sad that a freak accident in the paddock could claim the life of a 36 year old so quickly. Just sucks.

    I also lost my father the same week. Its complicated... but I didn't have much of a relationship with him, nor did my sisters. Still sucked hearing this news, which was unexpected. Throat cancer took him at age 75.

    And on that positive note... let's wrap it up!


    The "drive home from Nationals" always ends up where massive bench racing and planning happens, and this exercise is fun. I dreamed up no less than 4 cars "I need to build" for the 2017 season, two of which were CAM cars, but the reality is that... maybe one of them will get funded and built. I've got the manpower and the know-how to do more, just not the budget to build a fraction of what we can dream up.

    There are some plans for Mark's C5 still in process, which I'm not allowed to talk about just yet. I was going to bring his C5 back to Vorshlag after Nationals but Mark had an OKC autocross the following Sunday (today), so I dropped it off at his place and we will get our hands on it sometime in the near future.

    The pending rules changes (or not, we shall see) in CAM might prompt Mark to stay in CAM-S. If either the 650 pound penalty for C4/C5/C6 and Vipers goes away or they move to CAM-SS, he might stay in CAM. Otherwise he might move over to SSM and play with Hoosiers and aero. We shall see sometime in November when Raleigh releases any new rules for CAM. I will write up another entry here when we know more, or when get to play with this C5 - or another C5/C6 - in the future.

    Thanks for reading,

    Leave a comment:

  • Fair!
    Re: Vorshlag C5 Corvette Development Thread

    Project Update for September 11, 2016: After returning from the 2016 Solo Nationals I had a pile of work to catch up on, so I worked all weekend and then sat down to do my post-event write-up. It will be brief as we haven't done any work on the car since returning, and Mark still has to decide what class to run next year: CAM-S or SSM. I don't have anything poignant to say about 9/11, even after being at Ground Zero a handful of weeks after this terrible event (it was still burning) - other than to say "I will never forget". I also lost a family member while I was at Nationals, and two others from the CAM/Optima community passed away during the same week, so that's been a bit rough.

    There were some potential rules updates in CAM that were discussed and I will go over what was proposed at the Town Hall Meeting during Nationals. I drove pretty poorly and finished just outside the trophies, 7th out of 21 in CAM-S. Pretty disappointed in that, but the C5 ran solid and "coulda been a contender" with a better driver. Even with all of that we both still had a LOT of fun at Nationals this past week and I'm glad I went. It has been 4 years since I last attended - too long - but the fresh outlook of CAM is what brought me back.

    Photo and Video gallery:

    I usually take hundreds of pictures during my trips to Solo Nationals, but I had a bunch of stuff on my mind and just didn't take a ton this time. My wife Amy is usually with us and also snaps pics, but she didn't have a car to race this year and stayed home to work. The photo gallery above only has a little over 100 pics, mostly of the CAM cars, but also a few oddities we noticed during our 5 days in Lincoln.


    Most people don't live in Lincoln, Nebraska, so the vast majority of the 1350+ competitors at this year's Solo Nationals had to travel to this very centrally located event site, where the SCCA has held Nationals for the last half dozen years. For some folks (on the coasts) the trip spans days of driving or a transport service and a flight, but we brought Mark's Corvette up inside my trailer with our Ford F350 towing flawlessly. This truck is by far the nicest vehicle I own and has more horsepower (400) than any of my current race cars, which is kinda sad.

    From Vorshlag's Plano, Texas location, the trip to Lincoln was about 640 miles, which should take about 9-1/2 hours with no stops. I had to stop in Edmond, Oklahoma, to pick up Mark. Luckily that was almost directly on the way North to Nebraska. I left my house at 6 am Sunday hoping to get to the event site, unload the Corvette, and unhook the trailer before dark.

    We grabbed some breakfast in Oklahoma and kept driving north. Once we got into Kansas we drove for hours across this vista of corn and windmills, then we had a blowout on the trailer. GRR, I hate trailer tires, and replaced all 4 of them after I had 4 blowouts on the way too and from Miller for NASA Nationals in 2013.

    I know why this happened. Where I park my trailer on my property two tires are shielded from the sun by trees, but the other two (right side) get baked. I was suspicious of these two dry rotted tires before we left, but after replacing two front truck tires my "trailer budget" was pretty slim, so this blowout wasn't a huge surprise. We stopped within seconds of the tread cap coming off so it didn't do any damage. We installed one of two brand new mounted spares in a handful of minutes, and were back underway. #500psi

    Not 10 minutes later I got popped by a cop doing 63 in a 50 zone. I was really being careful not to speed, because I hate getting speeding tickets in these flyover states, some of which are known to fund their municipalities with speed traps. The Kansas and Nebraska highways have lots of changing speed zones, going from 70 mph to 55 mph and back again, quickly and seemingly at random - there's nothing out here but fields of corn!

    The rest of the trip was uneventful, other than pulling into a Kansas fuel station to be greeted by the bare ass of CP competitor Jeff Stroh mooning us as we pulled up to the truck stop pumps, LOL! We saw lots of fellow autocrossers traveling to Nebraska, of course. We arrived on site in Lincoln by about 5 pm Sunday and managed to unhook, unload, and get the Corvette through tech in less than 2 minutes (no line yet!). We also checked in at registration before the lines got too long on Monday. We parked 3 trailers from Texas racers in a circle to shield us from the unrelenting wind and inevitable rain.


    This was Mark's first Solo Nationals but I had been many times and understood the schedule. Monday is always when the Town Hall Meeting is held, which is one of the only times the members get to speak with the BOD, SEB and Advisory Committee (AC) folks face to face. I am not a huge fan of the way that rules get made, and have sent hundreds of letters to the SEB over the years, so I show up at these when I can.

    After a politically motivated shit storm following the 2012 Solo Nationals, I had walked away from the SCCA for the past 4 years, vowing to never build a car around SCCA Solo rules again. I've stuck to that plan, which has made my life easier. I do miss the challenge of Solo and as you have seen here in this thread, have dipped my toes back into the SCCA Solo scene in the past year. It was the brave new world of CAM that brought me back, so I wanted to go to the Town Hall to hear what was on the horizon for this category - to make sure that this set of classes stays as "un-SCCA" as possible.

    After some introductions and opening remarks by the SEB, they open the microphone to racers that want to bring up questions. Several sad pleas from SSR racers (this is a "throw-back" Super Stock class that still runs Hoosiers, that is quietly dying), and some talk about a potential revival of Street Prepared category with some "too little, too late" rules updates (this once popular category is also dying), we broke up into groups where the AC's met with members to talk about rules and trends at tables spread across the tent area.

    The wind was howling and felt like the tent would blow away at any minute, so we had to almost yell to be heard from 5 feet away (see video above). The "rules czar" of CAM, Raleigh Boreen, met with the interested CAM racers. We had a good discussion about the 3 existing classes. As many of you know, CAM is a very new category for SCCA, isn't (and may never be) "Nationally recognized", and the somewhat unlimited nature of the rules falls well outside of SCCA norms. That's why I like it - this isn't some 5 decade old category with old and busted rules, entrenched racers resistant to change, and is almost completely devoid of the politics that wrecks many classes over time. There is no "committee", which is probably why CAM has only one page of rules for 3 classes.

    Still, there were some concerns voiced by a few racers. "Money in racing" is always brought up, and the "have nots" always want an equalizer. Luckily that was largely ignored in this "builders class", so we moved onto other details. The existing rule for "+150 pound penalty for Lexan front windshields" was discussed, argued, yet most folks missed the point entirely (double pane safety glass windshields are safer, and side and rear Lexan windows are not a safety issue). Raleigh reigned that in and we moved on.

    So CAM is pretty simple: domestic front engine/RWD cars, some wheelbase limits, 200 treadwear tires, limited aero, and a minimum weight are all that the rules really care about in CAM. But the minimum weight in CAM-S (2350 lbs) is way lower than CAM-C (3200) and CAM-T (3000). CAM-C (newer with ABS) and CAM-T (older w/o ABS) are for 4 seat cars, and CAM-S is for the 2 seat cars with a shorter allowable wheelbase and ABS is allowed. CAM-S was supposed to be for real and kit car Cobras, and they can weigh about 2350 pounds in stock form.

    We lobbied to have the C4/C5/C6 Corvettes and Vipers added to the CAM category last year - initially asking for a 4th class called "CAM-SS" tailor made for these modern 2-seat domestic sports cars with a 2800 or 2900 minimum weight. We had hoped to keep this separate from CAM-S and the uber-light Cobras (and other CAM-S builds people can dream up, like tube framed ultra lights based loosely on some domestic car built in the last 115 years) and keep the min weight attainable without a tube frame build.

    At this town hall, Mark and I brought up the 650 pound penalty that is added to C4/C5/C6 Corvettes and Vipers in CAM-S. So we plead the case for moving these cars out of CAM-S into a new class called CAM-SS, and leaving the older 2 seat Corvettes (C3s are popular), Cobras, and lightweight custom builds in CAM-S. Or at the least dropping the 3000 pound min weight for them in CMA-S. Not wanting to rock the boat, we just wanted to follow the original plan for CAM: Classes separated by "old and new" + "4 seat and 2 seat" guidelines. Some CAM-S racers didn't want this, yet they don't want to race against "superior chassis with ABS" like the C5/C6 Corvettes. Some even suggested moving the C3 Corvette into CAM-T, which most CAM-T racers vehemently argued against.

    There were the "no rules!" folks, who oppose any changes, and a few weird arguments like "weight doesn't matter", arguing that the 2350 pound Cobras were somehow at a disadvantage because they were 650 pounds lighter - which I openly scoffed at. A handful of racers in CAM agreed that the 4th class, CAM-SS, would be best to move these modern ABS equipped cars away from the existing CAM-S classic cars. Hopefully this is the only change that comes of this Town Hall meeting, as the rest of the ideas just went in circles and didn't fix anything. Closing the 650 pound penalty in CAM-S still allows for the "crazy" builds but lets the more abundant C4/C5/C6/C7 Corvettes a place to race on a level playing field. Ultimately it is up to Raleigh, and he said he was aiming to have the 2017 CAM rules posted early - by November 1st or Thanksgiving at the latest - to give racers time to adjust for any tweaks to this new class.

    So we will see what becomes of that and Mark will decide where to take the C5 next soon after. SSM allows some big aero and of course Hoosiers. CAM-S has street tires, no aero, but seems more fun. And there are "damned rotaries" in CAM!

    The practice course is running most days during Nationals held on a separate part of the site far away from the grid and main course areas. The Nebraska Region SCCA runs the practice and it sells out weeks or even months ahead of Nationals. Mark thought ahead and bought a 4 run pass for us to use to get familiar with the concrete surface and maybe make some small changes to the car.

    We ran this on Monday before the Town Hall, with our 4 runs slotted from 2-3 pm. The wind was powerful and blew over the timers every couple of minutes, so in the 5 chances we had to check out the course we got no times on 4 of those. I got a somewhat lackluster time on my "sighting run", the first shot at the course either of us took, on cold tires. Instead of sticking around another hour trying to get re-runs on the 4 "no time" runs, we just packed it in and "saved the tires". I've made drastic changes based on runs from previous Nationals Practice courses and it always bit me in the ass. The car felt a little pushy, and we adjusted tire pressures UP from our local asphalt courses to this grippy concrete, but left the car alone otherwise.

    The rest of Monday was spent sitting around waiting for the course to be open for walk. We roamed around and got stopped by dozens of people, even ran into Brett Madson, who was my pick to win CAM-C (and he did, by a good margin).

    We walked the West course only, which was what we would be driving first on Tuesday. All of us scratched our heads at the unusual way that the course was marked. It was dominated by 3 cone clusters and cone walls, which I felt would lead to a lot of lost DNFs and cones (it did). On our first walk through we would find the #500psi cone, which was one that got pounded the most on this course.

    Bret's SN95 Mustang is pretty much a maxed out CAM-C build. It has a 2-valve 4.6L V8 that makes 380 whp (???). It is built light and has hundreds of pounds of lead in the rear frame rails, so that helps the front-to-rear bias greatly. It has a built T45, he runs 335 mm Rival S tires at all 4 corners, and uses modern Watts Link and decent spring rates. Nothing exotic, easily attainable, just one of the first folks to really build for CAM-C. He also drove his ass off and won the class by nearly a second.

    We ran across a lot of funny stuff in the paddock, like the fully furnished tent with hot tub in one area. The "Taco Truck on Every Corner" golf cart. Lots of wild SM cars with giant tires - a friend asked me to take pictures of the Subarus in SM, so you will see lots of 315mm and 335mm shod Subies in the gallery.

    The BRZ below left had a neat GoPro video camera mounted to a tow hook at the front, which I thought was a novel idea. This was one of nearly 150 of the "86 twins" that filled STX and CS classes. CS had 86 cars and STX had 72 entries, both with a very heavy BRZ/FR-S contingent. Giant freakin classes!

    After a long day of activities on Monday we headed to the hotel to check in. Mark had a room at a fancy Marriott downtown he got on hotel points, which was really nice. This was the first time I had stayed in a hotel in "The Haymarket", which is the downtown high end hotel, food and bar district. It is always where we end up going to eat during Nationals, and it actually makes sense to stay there if you are going to eat there - other than the F350 barely fit inside the parking garage.

    continued below
    Last edited by Fair!; 09-12-2016, 04:05 PM.

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  • Fair!
    Re: Vorshlag C5 Corvette Development Thread

    continued from below

    SCCA at Lone Star Park, July 30, 2016

    Event pic and video gallery:

    At this SCCA regional event Mark's Corvette had 3 drivers - Mark and Chase drove it in CAM-S while I jumped up to "X" class to run it in a different heat. And heat was the key word - it was 97°F during my runs and I forgot to bring my cooler - which led to heat exhaustion that day pretty badly (2 other people at this event went to the hospital that day, from the same effects). It hit me so hard that day that it has crept back and got me another 3 times this summer. I'm really trying to stay ahead of it by drinking lots of water and Gatorade type drinks, but heat is really killing me this year.

    You can't see it as much in the in-car video below, but I was fighting the ABS system in all of the big braking zones once again. This run the ABS completely goes bonkers on me and I blew 30 feet off line. The GM ABS is really starting to spook me - I just cannot use the brakes as hard as I can in a Ford, BMW or Subaru. Frustrating.

    The handling was much improved with proper rear compression valving set this time, and my raw time was pretty good on my 3rd run, but I clipped a damned cone again - just ran over the base. By my 4th and 5th runs my hands were shaking badly, I slowed down, and I knew I was in trouble with dehydration. That run heat took almost 2 hours and there was nowhere to hide from the relentless sun. By days end it was 104°F and I was close to throwing up. After the Corvette loaded in my trailer and I sat in the truck for 30 minutes with the AC on full blast, trying to regain control of my brain, with a pounding migraine from the heat exhaustion. I somehow got home, then drank a lot of water and passed out by 5 pm and slept for 14 hours. I felt terrible the next day, my whole body hurt. This was a bad day.

    My results in the "X" class were marred by my 3rd run cone (4th and 5th runs are thrown out in "X"), so I was somewhere near the bottom of the class. Mark and Chase ran in CAM-S a later heat but were about a second behind my best clean run. The rear tires were really giving up the ghost that day. They have been racing the car every other week all summer on this set, ever since the ProSolo, and did a huge number of runs on the rear tires. After this event we all decided the rear's needed to get bigger, so talked about an 18x12" rear wheel and 335mm tire for the remainder of the season.

    SCCA at TMS Bus Lot, August 28th, 2016

    Event pic and video gallery:

    This was last weekend's event, but the day before I was at Motorsport Ranch running baseline track times in my wife's 2013 FR-S. I got overheated and was feeling sick Saturday afternoon. On Sunday at the autocross I was already starting "behind" on my hydration, and heat exhaustion kicked my butt again on Sunday. This was getting ridiculous.

    I made a point to bring a stocked cooler with waters and Gatorade drinks and kept one in my hand all day, drinking non stop, but the previous day's damage was just too much to un-do. It wasn't even that hot, only about 90°F when I left at 2 pm, but I was feeling it while driving. I hit a record 6 cones over 5 runs in Mark's car that day, fought ICE MODE on every run, and had arguably my worst drive of the year. Right before Nationals, yay...

    This layout was what I call a "busy little Miata Course" - as are all of the courses at Texas Region events - but that's what we had to navigate in this car. Mark was ahead of me all day, and I just couldn't seem to get ahead enough on the courses or stay off the cones. I am not even showing my in-car video, its just awful. Mark, however, drove very well and put .425 seconds on me that day and pax'd top 20.

    We both felt the recent changes (see below) of new swaybars and wider 18x12" wheels/335mm tires made a big improvement out back. Mark's run above shows the Corvette doing so much better in corner exit than ever before.

    Running on fresh 315F/335R Rival-S tires, 18x11/12" wheels, MCS TT2 coilovers, Eibach bars, August 2016

    The MCS TT2 coilovers and new swaybars have improved the turn-in massively, and the roll/lean was visibly lower in head-on shots. Compared to the first time I drove the car on "good" tires, at the Optima event in 2014, its a night and day difference. That (below) was on 295/315 Rivals and Koni shocks with stock springs and bars. The new setup (above) has wider and sticker 315/35 Rival-S tires, yet radically less roll/dive/lean.

    Running on 18x11" wheels, Koni dampers, stock springs and shocks, and used 295F/315 Rival tires, April 2014

    So Mark was feeling good when we loaded up the Corvette that day, but I felt like crap again. And this was our last test event before heading to the 2016 SCCA Solo Nationals. I agreed to this months ago, but now I'm heading back to Lincoln for the first time in 4 years on a "low" for the season. I've gotta get my head in the game and stay hydrated next week in Nebraska. CAM-S is no joke at the National level. If anyone reading this sees me in Lincoln without a bottle of liquid in my hand, tell me to get some water!


    After the July event and before the August autocross we brought the car back to Vorshlag for some updates. After the August event we installed fresh front tires on the C5, in preparation for the Solo Nationals. I will quickly show that here.

    The aftermarket swaybar choices for the C5 aren't all that great, but we had supplied Mark's dad's C6 Corvette with an Eibach setup earlier this year. They were adjustable at both ends of the car and nicely built. So Mark wanted a set of Eibach bars for his C5. We ordered the C5 versions (no good pictures exist) and they showed up... non-adjustable. Oh well, they are tubular and larger in diameter, and Donnie installed them here with grease zerks and fitted the bushings to the bars so they can rotate (endlinks removed) with "pinkie effort". That's my rule on swaybars - no bind in the body mount bushings is allowed. Drilled, zerked, fitted, and greased every time.

    When I won a single BFG tire for my 2nd place finish at the ProSolo driving Mark's car I donated the winnings to Mark - it was his car, after all. We requested the Rival-S in a 335/30/18 size and rounded up two more 335s after they had run out of stock this summer (thanks for the hookup, whoever you were), which arrived the same day as the wider rear wheels.

    Earlier this year we saw some long lead times on custom Forgestar wheels, but this summer the wait times have shrunk as they invest in higher stocking levels of wheel blanks. A pair of 18x12" F14 wheels were custom spec'd rush ordered in "raw" finish (that can save you as much as 3-4 weeks) and mounted with the new 335s out back.

    The 18x12's have way more "poke" that I would ever spec for anyone, but Mark finally broke down and said he's commit to flared fenders - at all 4 corners - after Nationals. So we really ordered these 18x12" wheels for the front, but will use them on the rear for Nationals. Forgestar confirmed to me on the phone yesterday that they finally have 18x13" wheel tooling and these wider blanks should be arriving in October time frame. So the rears on this car will go to either 18x13" F14 or 18x14" M14 2-piece Forgestars. The car might switch autocross classes, too.

    The 315/30/18 Rival-S has been on backorder for many weeks as well, so we did some searching and Mark bought this set of 4 wheels and 4 new 315s mounted but never raced. Two of these became the "National set" of fronts.

    Running race compound brake pads makes the wheels dusty in a short time. One autocross and the red wheels look black (above). One of the things I'm always giving Mark grief about is how dirty he lets the Corvette get. He doesn't care - clean doesn't mean fast - but I keep reminding him that the giant "VORSHLAG" decal on the side means that I do care. So every time it is in my shop we seem to be cleaning it...

    We found a trick to cleaning metallic brake dust off of powder coated wheels years ago - a German chemical cleaner called "Sonax wheel cleaner", which I have mentioned here before. We have been ordering this stuff online and it is a bit pricey. Now there's a cheaper USA-made alternative called Code RED, which you can find at Pep Boys stores for about half the price per ounce. It uses the same chemical process that reacts to the iron particles in brake dust, which changes color from green to red once the process is finished. This must be washed off before it dries, and sometimes it takes two coats and some scrubbing, but its the best stuff I've ever seen for cleaning brake material off of wheels.

    Another pet peeve of mine with this car for the past year has been the unpainted front bumper cover. We replaced this when his previous co-driver had a big "off" and tore up the nose, but Mark wouldn't let me get it painted then. This time, as a condition of my co-drive, I insisted.

    Our friends at Heritage Collision Center in Sherman, Texas did a fine job and painted the nose and licensed plate cover back in body color. They had to do a bit of bodywork, as the unpainted nose took a lot of bug hits over the last year which damaged the surface. It looks as good as new now.

    Jon here at Vorshlag made some fresh "class/number panel" decals for the side and they classed up the car a bit from the hand cut tape decals (oiy!).


    We worked on some other things this summer, some of which are not finished, and I will talk about them after we readdress them after Nationals. For now we have the C5 as "ready as it can be" and loaded in the trailer. I leave for Nebraska tomorrow, picking up Mark along the way. I have no idea how we will do at Nationals, but I haven't been in 4 years and it will be fun to be there racing, win or lose.

    Vorshlag is also sponsoring the "Nationals Winner" jackets for all of the "supplemental" classes: CAM-C, CAM-T, CAM-S, and STP / STPL. These are all classes I feel are too important to ignore, and we have pushed the SCCA hard for two of these classes to be created (namely CAM-S and STP). I will do a write-up after Nationals and talk about the other systems we have been working on, as well as talk about the new autocross classing plans Mark has for this C5 in 2017.

    Last edited by Fair!; 09-03-2016, 04:52 PM.

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  • Fair!
    Re: Vorshlag C5 Corvette Development Thread

    continued from above

    Once the differential housing was attached to the transmission (above), then the torque tube could be reinstalled (below).

    Below are pictures of the hydraulic throw out bearing and the Keensert installation tool, for this thread diameter and pitch.

    With everything bolted together once again it was time to raise the transaxle + torque tube assembly back into the car.

    That all went back in place and the rear subframe then went in below that. The exhaust went on and we were ready to drive it.

    One other thing that happened while the Corvette was here that week were new front ball joints. The old ones were cooked (likely from brake heat + age). Toe was realigned of course. We changed the rears as well.

    Mark had also upgraded the front brakes to the AP 4-piston fixed motorsport calipers and 2-piece AP rotors, from their "sprint" kit, shown above. The rear brakes stayed intact.

    Test drove the car and the synchros seemed even worse in this "rebuilt" M12 than the worn out MM6 trans that we removed. Mark came into town and drove it and he noted the same thing - it was a hot mess. So out came the M12 trans and I took it our local Tremec specialist (Joe D) for an inspection. Joe opened up the trans and called - it was a mess inside. It needed everything from synchros to gears, shift forks to bearings, seals and blocker rings. Took some time to source all of the parts, but $2300 later it was rebuilt and ready to go back in. At least this time there weren't stripped threads and bolt heads that needed to be cut off - it went in painlessly and quickly.

    The race team that sold him this M12 owned up to some of the unreported damage, and I think Mark worked out some partial refund? The extra R&R work - since the transaxle had to come out again, get rebuilt, and be reinstalled - ended up as twice the normal install labor, plus the extra price of a rebuild on top of that. The C5 was also sitting for about 8 weeks while the trans was rebuilt then reinstalled, which sucked for Mark (no racing) and for my shop (storing the car for 2 months). Moral of the story is - always assume any used parts you buy need to be completely rebuilt!

    With the fully rebuilt M12 transaxle now in place, the Corvette was back racing in March. The new 1st and 2nd gear setup worked SO much better now, with 2nd gear speeds that are much more usable. The only time 3rd gear is needed are on GIANT autocross courses, which we sometimes see at Mineral Wells Airpark events - like the 2016 CAM Texas event and the 2016 Texas ProSolo (see below). At every other normal course, however, 2nd gear is the only gear needed and slower speed corners have more usable torque on corner exit.


    In May 2016, Mark wanted to improve the shifting of his car further so he ordered an MGW shifter from us. MGW shifters are made in the USA and the owners are super cool folks who road race regularly.

    Mark and his co-driver Chase managed to install this shifter in the C5 and ever since it shifts even better than before.

    With the long shift knob and the short throw shifter combined, the total shift throws are very manageable, the effort is low, and the "reach" for the knob from the steering wheel is a lot closer. Its a perfect shifter setup for this car.


    In an unusual move for me, I have raced in 5 SCCA autocrosses this year, all in various CAM class cars. I ran Scottish Joe's 5th Gen Camaro twice and Mark's C5 Corvette 3 times so far. I fought GM's ABS system "ICE MODE" programming at all 5 events, and it frustrated me a great deal. How isn't this more of a thing? Why does GM suck at programming their ABS schemes? The Ford ABS is light years better than the Corvette or Camaro ABS. When I brake hard the ABS on these cars often "freaks out" and just stops... stopping. Pedal turns to a brick and I blow through a gate or cone wall.

    2016 was the year of Cones and ABS Issues for me?

    I'm also pretty rusty when it comes to autocrossing, probably since I haven't done much of this in the past 4 years, but its coming back to me, bit by bit. Its tough for me to jump around in other people's cars, and my "cone count" is higher than it has been in years. I'm either ICE MODE'ing the brakes or clipping the cone bases (like above), so don't take my results and videos as an accurate portrayal of how these cars are handling - a faster driver can always make these cars look better.


    Event pic and video gallery:

    Vorshlag was an event sponsor for this CAM Challenge event as well as the Texas ProSolo, so since I was gonna be there to cook for people anyway... I found co-drives at both events in some of our testers' cars.

    Three Vorshlag test vehicles all running in the Texas CAM Challenge

    We were still testing a new setup on Joe's car and at the CAM only event, when it had fresh 305mm Hankook tires and new 19x11" wheels, where it still had a bit of a push.

    You can see the understeer we are fighting in the video above. One more event after a front spring change and more camber and we could have this one really dialed in.

    3800 pounds of fun and came in 2nd out of 19 CAM-C cars (with our shop manager Brad coming in 8th in the same car) at the 2016 Texas CAM Challenge, and damned if I didn't run the time to win in the brackets, but coned it. I lost in the Saturday runs by 1.4 seconds to an old friend and Vorshlag tester Brian Matteucci in his white 2015 GT, shown above.

    Mark and co-driver Chase were mired a good ways back in the CAM-S class, driving the C5 and fighting with "dead" tires. They were about 4 seconds slower than what we ran in the Camaro, which shouldn't be the case in an 800 pound lighter car. All year BFGoodrich kept running out of 315mm and 335mm Rival-S tires, and this was one of those periods where the C5 was shod with "compounded out" tires (I think they had 200+ runs on them at this point).

    No major changes were made to the Corvette before the next event, other than fresh 315mm Rival-S tires were mounted.


    Event pic and video gallery:

    I have co-driven Mark's Corvette three times this summer: At the Texas ProSolo in June, at an SCCA event at Lone Star Park in July, and at another regional in August. We are loaded up and heading to the 2016 SCCA Solo Nationals right now, too. I will give a brief overview of these 3 events so far in 2016.

    2016 Texas ProSolo:

    This was a fun event where I got to run the C5 in the merged CAM class for the Pro. Once again I was chasing Vorshlag tester Brian Matteucci's 2015 Mustang GT. Brian runs a Forgestar 18x11" CF5 wheel, 315/30/18 Rival-S, Vorshlag camber plates, GT350R springs, Eibach swaybars and a Torsen T2R diff with 3.31 gears - all of which we supplied to him. Brian is brutally fast in this S550.

    I kept fighting with the ABS system's "ICE MODE" and my best right side run had a cone after when the brakes simply stopped working in one corner. Sure, I can "brake less" and not engage this glaring fault in the ABS programming, but damn it you shouldn't have to drive around these issues in all GM cars. Why can so many other car makers program their ABS systems to work with a wider range of grip and brake pad compounds without issue??

    At this ProSolo Brian and I were paired up in the final 4 runs, and while I edged him by .3 sec in time overall for both sides, he beat me by .3 sec in the paxed times. The Corvette was really loose on corner exit at this event, and with the hectic nature of ProSolos (you run 2 left and 2 right side runs back to back) there isn't time (nor are you allowed) to change shock settings between runs.

    Come to find out later, the rear shocks were set at an incorrect amount of compression, and we didn't catch it until after my runs were over. No wonder why it wouldn't launch well or put power down on corner exit. My runs were filled with lots of little driving mistakes, and I didn't have a single 4 run grouping without a major ABS brake system failure and subsequent "cone binge". I could not reprogram my brain to brake more gently than I am used to in autocross situations. The S197 Mustang ABS system ruined me, I guess? At least a Vorshlag tester took the win and the top 5 out of 7 in CAM were Vorshlag test cars once again.

    continued below

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  • Fair!
    Re: Vorshlag C5 Corvette Development Thread

    Project Update for September 3rd, 2016: Mark has been having a blast with his C5 Corvette over the past 10 months, other than a transmission issue we fixed . There's now a newly rebuilt C5 Z06 transmission in and the improved gearing was a huge improvement over the base C5 transaxle. Shifter has been upgraded to an MGW from a Hurst, and more motorsport appropriate AP brakes were installed up front - their lightweight 4 piston Sprint kit with 2-piece rotors.

    Mark and co-driver Chase have driven the car numerous times this season in autocrosses from Dallas to OKC. The car has bounced back and forth from SSM (on Hoosiers) to CAM-S (on BFG Rival-S tires), on the 18x11" Forgestars with 315mm tire sizes. I've autocrossed in this car a number of times, too, so let's get caught up on this C5 Development thread.


    The gearing for 1st and 2nd gear were not working well for autocross use in Mark's "Coupe" 6-speed car. Remember - his C5 is not a C5 Z06, which has different transmission gearing for 1st thru 3rd gears (and 5th and 6th as well). Let's dig into some tech here to clear things up.

    There were actually 3 different transmissions (technically - "transaxles") and 3 different final driver ratios used in the C5 generation Corvettes (1997-2004). There are also some extra names for some of these transmissions - mash-ups of two RPO codes - as well as redundant RPO codes (2 codes for the same thing) to make it all extra confusing. Below are the actual GM RPO codes for the C5 drivetrain options, based on this this link and interweb research. I'm not even going to touch on the C6 stuff, which is similar but different.

    RPO option codes for C5 Corvette transmissions ans final drive ratios:
    • MM6 Transmission, Manual 6-Speed, 85 mm, 2.66 1st, 0.50 6th, O/D
    • M12 Transmission, Manual 6-Speed, 85 mm, 2.97 1st, 0.57 6th, O/D
    • M30 Transmission, Automatic 4-Speed, 4L60-E, Electronic
    • GU2 Axle, Rear, 2.73 Ratio
    • GU6 Axle, Rear, 3.42 Ratio
    • G90 Axle, Rear, 3.15 Ratio

    These are codes that confuse people, because they are completely redundant
    • G92 Axle, Rear, Performance Ratio (this just means the car has an "optional ratio")
    • MN6 Merchandised Transmission, Manual 6-Speed Provisions (means it has a 6 speed manual)
    • MX0 Merchandised Transmission, Automatic O/D Provisions (means it has an automatic)

    The Borg Warner "T56" (that one is not an RPO code, but instead a model name from BW) 6-speed M12 code transmission was the only gearbox offered in the C5 Z06 and the MM6 code was the other 6-speed manual offering in the Coupe and Convertible. The M30 (also known as the 4L60E, and shorthanded as "A4" by some internet folks) automatic 4-speed transmission came with a tall 2.73 (GU2) final drive ratio but there was an optional (G92) 'performance' ratio of 3.15 (G90) that could be ordered on that car. All 6 speed manuals in all C5 Corvettes came fitted with a 3.42 (GU6) final drive ratio. The differential housing (on the back of the transaxle, which holds the final drive ring and pinion + limited slip differential) for the 3.15 and 3.42 ratios are larger than the base model automatic's 2.73 housing.

    There were other changes with the C6 generations, which all had more powerful engines (LS2 = 400 hp, LS3 = 430 hp, LS7 = 505 hp) than the equivalent models of C5 generation (LS1 = 350 hp, LS6 = 385 then 405 hp). Mark's C5 has a slightly modified 5.7L LS1 engine (camshaft + headers + cold air) and makes 425 whp on a chassis dyno, so that's roughly 475 hp at the crank.

    The video above
    has sound clips from this C5... sounds meaner than "slightly modified"

    Here are the two main 6-speed transmission gear ratios, by RPO model:

    M12 (Z06) 6-speed gear ratios:
    First: 2.97
    Second: 2.07
    Third: 1.43
    Fourth: 1.00
    Fifth: 0.84
    Sixth: 0.56
    Reverse: 3.28
    Final drive ratio: 3.42

    MM6 (base C5 Coupe and Convertible) 6-speed gear ratios:
    First: 2.66
    Second: 1.78
    Third: 1.30
    Fourth: 1.00
    Fifth: 0.74
    Sixth: 0.50
    Reverse: 2.90
    Final drive ratio: 3.42

    The Z06 Corvette's M12 has lower gears (higher numeric ratio) than the MM6 for gears 1-3. Fourth is the same for both. 5th is lower and more usable in the M12. 6th gear is never used for performance driving - it is the mega-driver highway gas mileage gear, which is only slightly different between these two models.

    Calculations for speed in each gear, 3.42 final drive, M12 vs MM6

    The goal in all autocross cars is to optimize speeds in 2nd gear, which is the gear used almost exclusively for the majority of the time spent on most courses. The goal is to achieve a terminal speed of most courses usually between 70-75 mph. Racers will run speed-in-gear calculations (as shown above) with their max engine RPM (7000 in this case), tire height (25.5" tall for 315/30/18 tires), final drive ratio (3.42:1) and the gear ratios in each gear for the transmission. As you can see 2nd gear on the MM6 transmission in Mark's car goes all the way to 87 mph! That's faster than the top speed in virtually any SCCA autocross you will ever see. With the Z06's M12 6-speed swapped in, however, 2nd gear goes to 75 mph. This is damn near optimal for 90% of the autocrosses you will ever see. With a 75mph terminal speed in 2nd gear that means the Corvette will be also geared better on more courses for all speeds under 75mph.

    But changing the transmission in a C5 Corvette is an expensive job - both the parts and the labor (8-11 hours is often quoted just for the R&R). Finding a known good used C5 Z06 "M12" transmission is also difficult, as these are no longer sold new. You would normally have to source a correct used M12 transmission (money), then have it refreshed (more money), then have it swapped (time and money).

    Option 1 to "fix 2nd gear speeds" change would be to alter the final drive ratio by changing the ring and pinion in the differential. The common change is to a 4.10 ratio, which will lower 2nd gear speeds closer to the speed range we want. Changing the final gear ratio in the differential is much more expensive to do in a C5 than in solid axle RWD cars like a Camaro or Mustang, where you can buy the ring and pinion set for under $200 and have them installed professionally for $350-500 in labor/small parts. On a C5 Corvette, which has a rear transaxle, you end up paying around $2000-2500 for parts and labor to change the final drive ratio. That's just how it goes, no short cuts or cheap parts here.

    Option 2 is to change the transaxle out completely, from the MN6 to M12 geared 6-speed. This will always cost more, because it takes more labor (9+ hours) and the parts cost more ($3000-3500 for a core M12 trans + a rebuild is common). But in the case of Mark's car, where 4th gear synchros and mean gear cluster were worn badly, this was the right way to go.


    Since Mark knew his Corvette's original MM6 had a blown 4th gear and needed to be fully rebuilt, he took the plunge and went for the M12 transmission swap. This was a better route than going for a rear gear change + upgraded differential + MM6 transmission rebuild.

    Mark found a great deal on an M12 transmission that "had just been rebuilt" from a race team, made the deal, and had it shipped to our shop. He paid a good bit for it, due to the freshness of the rebuild, but it seemed like it was overall going to be cheaper than what we could have done for an M12 core + a proper rebuild + the trans swap combined.

    We normally have a policy of not allowing customers to bring us used parts to install. Why? Because if a customer supplied a part, we install it, and the parts turned out to be junk, we aren't liable for the re-work to fix it. Even though we didn't supply the parts, that situation always makes the customer upset. We have learned this the hard way - and that it is the right policy for shops to stick by. Mark has been a great customer, so I bent the rules this one time... let him bring us parts, but I warned him if the parts weren't any good the labor to fix it "was what it was". He understood and took the risk, with the benefit of that he might save up to $1000.

    To remove the C5 transaxle you have to drop the rear subframe as a unit along with the "torque tube". This is the aluminum tubing section that houses the driveshaft inside and bolts to the bellhousing and transaxle. The clutch is up front like a normal front engine car but the transmission and diff housing (transaxle) are mounted out back.

    Of course nothing went according to plan, on the car we originally coined the "eBay Corvette". One more janky piece of previous mechanic work from the past bit us. There are several bolts that normally thread into the bellhousing which hold the torque tube in place. Three of these were stripped - it took almost no effort, but these three would just spin and spin. But they wouldn't come out...??

    We realized later that instead of threading into the housing, the holes had been stripped out and nuts had been super glued to the inside. That temporarily held the nuts on the inside of the bellhousing, just long enough so they could be snugged up and impacted tight. And while you technically can tighten a bolt and hidden nut this way - once - the bolt won't come apart without cutting the heads off. The glue had long since stripped out, so when the bolts were touched to loosen them, they just spun and spun. Cutting the bolt heads off took some time, as did the installation of three Keenserts to fix the stripped threads in the bellhousing. This is a type of heli-coil but with 4 teeth that you use a special tool to set into place. Super strong, fix it once, and forget it.

    Once those 3 bolt heads were cut off the remaining hardware was removed and the transaxle + torque tube could be dropped out. Then it went on the bench and we started transferring the torque tube and rear mounted differential unit to the "new" M12 unit.

    This was another strange "fix" we ran into when disconnecting the shift linkage. There was a bolt that had been tack welded to the shift rod coming out of the transmission. This rod had all sorts of hacked up marks on it from a previous mechanics work with what appeared to be a chain saw. We cut the welds loose, cleaned up and welded the deep cuts on the shift rod, and replaced the hardware with new parts.

    Since both the M12 and MM6 used the same differential housing and 3.42 final gear we just unbolted the back diff section from the old (MM6) trans and bolted it to the "new" (M12) trans.

    continued below
    Last edited by Fair!; 09-03-2016, 04:41 PM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    continued from above

    Polyurethane Bushing Upgrade

    This next round of work was no fun to do, but it will make an improvement in performance. Since the front right lower control arm had shifted in the incident it needed new bushings, at a minimum. And with over a decade of time and use the rubber suspension bushings were looking a little ragged, so it was time for poly.

    Replacing rubber suspension bushings (especially hydraulic filled ones) with firmer durometer polyurethane material is an old racers trick, at least for cars that cannot use Delrin or metal bushings. This C5 is one of those "tweener" cars... it is a dedicated race car that is trailered to events, but... it might someday end up in a racing class that forbids metal bushings. And metal bushings have a higher wear rate and are always noisier. Properly greased, poly bushings can be silent yet remove the majority of rubber bushing deflection under cornering and braking loads.

    Using heat (propane torch), pressure (30 ton press) and elbow grease the OEM rubber bushings were removed from all 8 control arms. These things are bonded to the aluminum so the heat is necessary to get them to come out.

    Getting the new poly bushings in place takes pressure (press) and patience. This is tedious work and gobbled up hours of time. There is one important step next that many people ignore...

    Grease zerks were added to every bushing location. This involves drilling the control arm and tapping it for the grease zerk. With 1-piece poly bushings you also need to drill through the bushing, so grease can get on the inside, next to the sleeve it rotates on. Then line up the holes (2-piece split bushings usually have a gap in the middle that grease can pass through). This ensures that if the bushing grease pushes out over time (it will) it can be re-lubed to quiet that joint. A dry polyurethane suspension bushing not only makes noise it adds "stiction" to each joint.

    A little forethought must be used to map out where the grease zerks should go - don't just go drilling holes willy-nilly. Think about how the control arm will sit at ride height, full bump and full droop. You don't want the zerk getting bound up on the subframe and getting snapped off. You also tend to grease these with a car on the lift at full droop, so leave yourself access room for greasing them in that suspension position.

    All told this was over 10 hours of work, but likely something that will never have to be done again. Again, with proper lubrication these should give at least a decade of silent use.

    An example of why this is necessary: We had a Miata that came in our shop about 2 years ago that we installed poly bushings on. We had started adding grease zerks (to the front control arms points) but the customer didn't want to pay for that, so we stopped at only the front bushings. I should have insisted - two years later one of the rear bushings was worn out because it was dry (had not been lubricated). These poly bushings should get a little squirt of grease every 6 months or so, sooner if they make any squeaks. Its back at our shop now getting grease zerks added to the other joints today, after replacing the bad bushing.

    Spherical Lower Rear Shock Mounts

    The only rubber left in the suspension at this point was the rubber lower shock mount for the rear. It was a big honkin bushing, and that will deflect under bump loads - delaying the damper reaction as well as the spring.

    We looked for a solution and found one from Pfadt, which is owned by someone new lately. I'm not a big fan of their shocks or other parts, but they seemed to have one of the only spherical conversions for this shock mount, so we went with it.

    This was relatively easy to swap out since the rear lower control arms were out of the car getting poly bushings at the pivot points on the subframe. This Corvette is now rubber bushing free in the suspension.

    Steering Column Lock Defeat

    Like all factory built cars, the C5 Corvette has a theft deterrent in the steering column where if the key is removed or turned to the off position, the steering wheel "locks". This makes it harder for a thief to drive your car if he "hot wires" it.

    But when you are racing and, say... you lose the brakes.... drivers are taught to kill the motor, and let engine braking (an engine is just an air pump, once you remove fuel and spark) help slow the car down. But if you do that with a stock steering column, and go past "off" on the switch, you just lost the ability to steer. After you lost the brakes. Not a good situation to be in.

    Normally whenever we are prepping a race car there is just a mechanical "pin" that locks into the steering column, which we can drill out or remove. But GM had to get fancy and make a motorized doo-dad that did the same task. This is driven by a Body Control Module, but this system is a well known failure point - leaving you unable to steer your car after started-up and limiting speed to 2 mph while driving with the locked column. And of course, after this many years, this car's steering interlock system started to flake out. When it would do this, the steering wheel would lock after you started the car, and you couldn't steer. So.... yea, that needed to go.

    We could have ripped apart the column to find the interlock motor but that causes other problems. So instead we ordered the LMC5 Module shown above, which is a kit to electronically disable the electro-mechanical steering interlock system.

    It has to be wired in under the dash but Brad managed to knock this out in 1.75 hours, while standing on his head. Now the GM system is removed and the steering wheel can always be turned. A better theft deterrent is removing the wheel altogether...

    Header Repair + Rear Exhaust Hangers

    The header repair was pretty basic, but it was tricky to do with the header attached to the car. Ryan made a template of the mashed in bits then cut out the smashed section...

    Getting that cut out cleanly while still in the car was tricky. He then took the template and transferred it to some stainless 1.75" tubing. The round patch was then TIG welded over the hole in the primary tube for a repair.

    A rear exhaust hanger was broken in the "off" so both rear hangers were also replaced.

    A Move To 315 Rival-S Tires

    Last but not least Mark wanted to try a set of 315/30/18 BFGoodrich Rival-S tires. Why go from A6 Hoosiers to 200 treadwear Rivals? Well there's reason to believe that the CAM category in SCCA Solo might grow next year to include CAM-SS. Not to mention these tires give him the opportunity to race with both USCA/Optima and Goodguys, which are on his list. Mark has already run the C5 at Goodguys, since he picked it up.

    Currently the CLASSIC AMERICAN MUSCLE (CAM) category encompasses 3 classes, but the C4-C7 Corvettes are excluded. You can see the basic CAM rules here. There's talk (and we've written letters) to include the newer Corvettes in their own CAM class called "CAM-SS" for 2016. If so then Mark wanted to have a tested setup ready to go on Day 1.

    Olof removed the dead Hoosiers from the 18x11" Forgestars and mounted up the 315 Rival-S tires. Brad cleaned the wheels with some pressure then some SONAX wheel cleaner to get the rest of the brake dust off. That stuff is magic... it turns color when it reacts with the metal in brake dust.

    Speaking of brake dust, the reason there was so much was because the pads were gone. The old HP+ pads on the left and new XP12 Carbotechs on the right. Olof swapped in these new pads all around.

    All Fixed - Ready To Race

    After all of this work was wrapped up, the Corvette was ready for autocross action once again. We cleaned up the whole car for Mark - since he never washes it!

    One little freebie we threw in this time was the new decals. Since Mark's co-driver paid for the front end damage repairs, so we figured the least we could do was make him a sponsor decal.

    More Autocrosses + What's Next?

    One of the first event's Mark did after picking the car up was a local autocross, which he used to get the car dialed in on the Rival-S setup. He then entered the All American Sunday (AAS) autocross class as the October Goodguys event at Texas Motor Speedway

    He was leading all day and into the last runs, but then Aaron Sockwell snuck past him on their final runs to take first place, with Mark in 2nd. Tough loss, as 1st pays out a free set of tires and all sorts of swag at Goodguys. Aaron drive's a 2015 Mustang GT that we also used for suspension development on the S550 chassis. It also sports red 18x11" CF5 Forgestars, 315 tires, MCS TT2 doubles, and Vorshlag camber plates. Aaron also ran this course on Friday-Saturday in a customer's 67 Mustang, so he had a little more experience on that course.

    He has been running the car in more events since and having a ball.

    At this point I have no idea what Mark will want to change next, if anything. The suspension feels great now and shouldn't need much from here on out. The motor makes great power but it could always make more, of course - just costs money! The gearing is a bit mismatched for autocross speeds, so a rear gear ratio change might be in the cards.

    Of course I'd still like to see the move to BIG wheels and tires, but cost of the flares and the labor are up there. Who knows, this might be this car's final form for awhile. And that's not a bad thing.

    Last edited by Fair!; 10-12-2015, 05:29 PM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    Project Update for October 12th, 2015: Well some things happened to the C5 that changed the priorities for a few upgrades. The intended budget for flares and wheels was instead spent doing some repairs to Mark's C5 in august, but luckily he was wise enough to let us work in some upgrades while the car was apart at our shop.

    A co-driver took Mark's C5 for a ride through the weeds, way off course at an Autocross over the Summer. While the off-course excursion was underway the only thing within 100 feet that could damage the car was hit - a big, steel propane valve.

    I don't have good "Before" images, as our crew stripped the front end right after the car arrived, to assess the damage underneath. The front bumper cover was destroyed, as you might imagine from these structural pics, but the frame, subframes, wheels, exhaust, and the rest of the bodywork were unscathed.

    This propane valve was poking up out of the ground about 6 inches and dug a hole through the front end, then tore up a number of things under the chassis. The bumper cover was shredded, the tubular front bumper support structure was twisted like a pretzel, the radiator and condenser were smashed, one of the control arms was pushed back, and a header primary was crushed.

    This car was lucky - it could have been a lot worse. The car sort of V'd into the valve, then when it dug into the front end it pushed up and "jumped" up over it, so nothing behind the header collector took any further damage. The valve was rock solid, so the car could have sustained more structural damage to the floor and rear suspension if it hadn't have "jumped up".

    I don't know much more about the incident, so don't ask. Yes, it is very rare for a car to sustain damage at an autocross - this is still the safest form of motorsport I know of this side of video games. It was a new site they were using for the first time and his co-driver just... "lost it". Going fast. Luckily Mark had invested in a truck and trailer, so he was able to winch it up on the trailer and drag it down to us, without having to call a flat bed wrecker.

    Crash Repairs = Perfect Time for Carbon Upgrade!??

    With the front bumper cover and structure wiped out I thought it might be a good time to go ahead with the previous plans of a splitter, ducted hood, and carbon front end.

    One possible way to "fix" the damage was this upgrade, but it was pricy

    I tried hard to get Mark to upgrade the front to C5 carbon fiber nose + splitter + ducted hood made by AJ Hartman (see above). Looks so good, but there's a lot of fabrication required to make it all bolt up.

    We're a dealer for AJ's parts and love his carbon work, so I worked up a good quote for Mark... but it was still pretty pricey. Part of the estimate was a big "unknown" - the custom structure needed (see above) to support the splitter, heat exchangers, and bumper cover.

    Plus to work with AJ's ducted hood the intake manifold has to be flipped 180° and the throttle body is then fed from the cowl, which entails more modifications and unknowns. Try as we could, I just couldn't give him a solid enough estimate he could live with. But hey, I tried!

    Front End Repairs and Upgraded Radiator

    The C5 stayed at our shop while we assessed the damaged, ordered parts, did repairs, then did some nice little upgrades.

    Finding the bumper cover and front radiator/skid plate structure was pretty easy. The new bumper cover is a good bit lighter than the OEM bits (typical with Taiwanese replacement parts) and Olof took the badges off the stock piece and transferred them over.

    The new square tubular structure that holds the radiator and bumper in place is a pretty lightweight piece, but it comes in bare steel. The old one was rusty and we didn't want that to happen to this one, so we cleaned it with Scotch-Brite and wax & grease remover, then painted it with 3 coats of semi-flat black enamel paint.

    As that went in the car, so did a massive all-aluminum DeWitt C5 radiator. This thing is 2x as big as the core on the OEM unit, and didn't have plastic end tanks glued in place. That's good for both cooling and reliability upgrades.

    A new A/C condenser was attached to the radiator, which took a little modification since the new rad was so much thicker. But it still fit within the confines of the two original equipment heat exchangers and the unit slid back in place nicely.

    With the old (destroyed) radiator out of the way we noted some crusty, nasty funk inside, as well as the water pump inlet and outlet. This seemed like something worth showing to Mark, so the picture below was sent and followed up with a phone call...

    Apparently even the fancy GM anti-freeze isn't perfect, and 13 years of use had led to a lot of deposits in the cooling system. We could flush out the engine pretty well, and it was getting a new radiator, but we felt a water pump + thermostat + t-stat housing replacement were a good idea.

    Mark agreed and since the front of the car and radiator were both out of the way this was an easy water pump swap, adding very little time (a whopping 30 minutes).

    There were little wiring repairs, riv-nuts that had to be reinstalled in the frame (see below), and lots of little "fiddly bits" to fix, but it was straightforward.

    The front end repair and radiator install only took about 5 hours of labor, which isn't bad considering how much damage there was.

    The lower air dam was replaced with OEM plastics, as the old ones were worn from time and torn up even more in the incident. Luckily the aluminum front subframe wasn't damaged, so it was left untouched. We're not a body shop so the front nose was left in bare ABS black when it left, but Mark said he had a guy that would wrap the car soon.

    Two of the tie rods were looser than before, and all four were original, so we suggested replacing the outer tie rods at all four corners. This was actually very easy as we had the suspension apart for bushings, shown below.

    continued below
    Last edited by Fair!; 10-12-2015, 06:40 PM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    continued from above

    One more thing to note about this event - the sound readings were great on the C5 and we never blew 100 dB all day, while many others did. I noted some 93-97 dB readings for our two entries (SSM 105 and 5), but nothing out of the ordinary. This site is not sound restricted but many autocross sites are these days, and I was worried the side exhaust might not do well for sound readings. We were topping out 2nd near the sound meter, so it wasn't the best conditions for this car to "blow low" sound, either. I love it when we build an exhaust that can reduce noise levels AND make a +50 ft-pound torque bump in the mid range +25 whp up top.

    What's Next?

    So Mark has spoken with me in the last week and is throwing us a bit of a curve ball - it now needs to do well at autocross as well as track. These two motorsports don't exactly share the same requirements, but many of the improvements we had planned can work well in both formats. I have conferred with Jason, Brad and Jon at our shop - all experienced autocrossers, and we have made some suggestions on his new plan.

    Of course I told Mark my opinions about using "scrub tires" and that if he wanted to get more serious with the car for autocross events it needed fresh tires in wider sizes. If he wants to make it more track worthy, we could likely stick with these tire sizes for a bit and concentrate on aero. Especially for his home track Hallett, which has a few quicker corners (T1, T4, T8-T9) where aero will help. So he had some deciding to do.

    We had all initially planned on attacking aero upgrades next then attacking wheel/tire width down the road, but we are skipping ahead a step now. Yes, Mark still wants to do the the giant splitter, diffuser, AJ Hartman ducted hood and rear wing - but these will wait until after adding some mechanical grip by way of wider tires first. Why? Well he's going to be doing more autocrosses than road course events right now. Since he's the Regional Executive of the Oklahoma SCCA Region, which does a lot more Solo than Club Racing, he ends up at more autocrosses. So his car is being forced into a more autocross-centric role, at least in the short term.

    The end goal is still the same - NASA TT2 - but anything that can help that goal PLUS make it quicker in parking lot events will come first. Unfortunately the September Hallett track event Mark had planned got scrubbed due to a work trip that popped up, so his first track test will have to wait a bit, but he does 2-3 autocrosses every month already. So now Mark is scheduled to bring the C5 back to Vorshlag at the end of the summer to allow us to explore ways to fit larger wheels and tires to the C5... namely some 18x13" front and 18x14" rear sized wheels, likely in the model shown below.

    The new Forgestar M14.2 wheel is a 2-piece design we first reported on at SEMA 2014, and we were told about them before that after talking to the principles at Forgestar about our BMW E46 LSx race car we're building for the 2016 season. These M14.2 wheels are being made in 18x7" to 18x15" widths, in half inch increments, and they are more cost effective than 1-piece monoblock or 3-piece wheels in the wider widths (final pricing has not been announced at this time, but its supposed to be a good bit less than $800/wheel).

    When it comes to autocross and track handling, the axiom "BIGGER IS BETTER" applies to tire width

    After years of working my way up in tire sizes on various autocross and road course builds, I'm convinced that nothing performs (via adds mechanical grip) better than TIRE WIDTH and compound. We noted incredible improvements (2-3 seconds per lap, at the same tracks) from the 2013 to 2014 seasons on our TT3 Mustang after switching from 315mm A6 tires (2012-13 events) to 335F/345R Hoosiers (2014-15 events). So we're going to PUT 345s ON ALL THE THINGS!

    Seriously, this 345/35/18 Hoosier A6/A7 tire is freagin MAGIC. Nothing matters more than tires in racing, and nothing beats this big monster. Its the biggest DOT tire Hoosier makes, and personally I want this tire on the back of everything I drive in autocross or road course events. Mark seems to think it will work on his C5, and I couldn't agree more. He fought for both front and rear grip on the 295F/315R Hoosiers at all three autocross events he has done so far, and going +30mm on the rear and +40mm on the front will very likely make the car faster and easier to drive. Isn't that always the goal?

    A little bit of this, and little bit of that...

    How do we get these wheels to fit? Well we'd like a bolt-on composite set of flares (fender overlays) for a C5 that are a cross between the bolt-on aspects of the Liberty-Walk type kits (above left) and the function of the C5R bodywork (above right). We can't just go out and order up some C5R bodywork - it was made to mount to a semi-tube framed car, and is long out of production. So we need to MAKE something. Which is a big task, and we will need outside help here, but we're gonna try. Why? Because nobody makes flares for a C5 to fit this much tire - yet. And the car needs real flares to properly cover the front and top sides of these MASSIVE wheels and tires - to keep the spinning tires out of the airstream.

    Fitting 315F/335R tires requires a lot of poke (left) and some fender cutting. C5 rear flares don't cover much more tire (right)

    I've seen numerous C5s try to run wider than the 295F/315R sizes. We found that to be the limits under the stock fenders, which Mark's C5 already has. Stan Whitney's beautiful XPrepared C5 (above left) had 315F/335R tires, but like all C5 racers using these sizes, the tires stick out of the bodywork (poke). To keep from cutting the tires they cut the fenders upwards for bump travel clearance. This trick works for autocross speeds but doesn't work well at road course speeds. Similarly, the "hard parking" flare kits (above right) we've seen offered for the C5 only seem to cover the tops of a marginally wider tire, and barely have any bump travel before they rub. These also leave the front of the spinning tires sticking out in the airstream - which is a drag.

    Mini-tub conversion on the rear was discussed, but judged to be not worth the effort or class penalty

    We talked to Mark early on (and mentioned it in my first post) about mini-tubbing the rear, but after researching this further, there are three serious limitations on adding wheel room with minitubs on the C5 chassis. First, there isn't much wheel room to be gained inboard on the rear (1" of width), as the rear suspension control arms quickly become a limiting factor. Second, it is a lot of work/expense for very little gain in width. The most you can do with a mini-tub job on a C5 is a 19x12" wheel (18" wheel barrel hits the control arms sooner) so it is not much help. Third, modifying the inner fender/tub isn't legal in many racing classes, or incurs a "non-production chassis" power-to-weight ratio penalty, like in TT1/2/3 (see below).

    7.3.2 - Restrictions and Limitations for Production Vehicles

    A) Other than the listed exceptions, every Production vehicle must retain its unmodified:
    1) OEM frame rails/rear frame cross beam, and/or Unibody, and Sub-frames/
    suspension cross-members (in their OEM locations)
    2) Strut/shock towers
    3) Inner/inboard side of the fender wells (any non-horizontal aspect)
    4) Rocker panels
    5) Transmission tunnel
    6) Floor pan
    7) Windshield frame location

    7.4.2 Modification Factors (TT1/TT2/TT3 only)

    The “Modification Factor” listed after each item below is added or subtracted from the actual measured Wt/Hp ratio to determine the “Adjusted Wt./Hp Ratio” that determines vehicle legality in each TT class.
    • Non-Production Vehicle: TT1 & TT2 = -0.4
    • TT3 = -0.7
    The rule listed above is straight from the 2015 NASA TT ruleset. It might not seem like much, but a -0.4 ratio penalty is rough. Consider that as a TT2 car this C5 will have 7.9:1 pounds per hp ratio limit (with a +0.1 bonus for running 3300-3399 pounds comp weight), but the minitubs would knock you back to 8.4:1. On a ~3300 pound car like this (with driver) that -0.4 penalty equates to 20 whp you would have to give up or 165 pounds of additional ballast.

    I'm used to making wide body flares in steel, and if you've read any of my forum posts since about 2006 you know this. But fiberglass... ? Man, I hate working with composites. Fiberglass is a messy, stinky, nasty material to work with. And when you cut or sand this stuff it makes a dusty, itchy mess that gets everywhere, including in your lungs and the pores of your skin. But... its the only thing that makes sense on a car with a body entirely made of fiberglass. Yea, yea, yea, your buddy is good with carbon fiber, which is bitchin' and all, but not practical for low volume production or one-off flares. I've worked with CF and its an expensive, complicated, messy, stinky, nasty material to work with!

    First we need to get the wider wheels/tires on the car (left) and clearanced. Then (right) flares are built around them... "Easy!"

    Once we have some sort of foam/wood/fiberglass bucks built up on the car, we will work with a mold maker friend of mine to hopefully make short production runs of something we can replicate - hopefully. I'll post up any news here, so don't ask me a thousand times what they will cost or when they will be ready for sale. I have no idea, but if something goes into production it won't be introduced in secret. Read this thread and you will now the latest on whether this worked for production or if we just made the one set for Mark.

    That's all for this time - thanks for tuning in!

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    Project Update for July 17th, 2015: Short and sweet update this time, after another autocross test event (where we got more than one run) and a slight change in priority of the build, but its pretty cool.

    Mark's C5 has been driven in anger four times since he bought it - at Optima on street tires, at the June autocross on Hoosiers, another June event in Oklahoma, and now at this July event. The last 3 events were on the new suspension we built and installed and there are some good comparisons I will show below. The last 3 events were also on the same (used to begin with) set of A6 Hoosiers, which began to fall off a cliff and lose performance due to heat cycles and age. It is always tough to test on less than ideal tires, so we didn't make radical changes. I'm still waiting to see this car on a road course - which is what we all agreed that it would be intended for in the first place.

    Let me just start out with the obvious - summers are HOT here in Texas. We had a bit of a reprieve from our normal super hot June-July-August months with unprecedented rains from early Spring into July this year, but this past weekend was back to "normal" for us - sunny, hot, and humid.

    It was perfect weather for a Vorshlag pool party the day before this autocross event, which we had at Brad's pool. Started at 3 and I wasn't home until midnight, and we all ate and drank our fill. That 5 am wake up alarm on Sunday for this autocross was brutal. Once again Amy left me to my own devices, and wisely passed on autocrossing at this event herself.

    Texas Region SCCA Event, Aug 12, 2015

    I arrived at the Texas Motor Speedway event site at 7:05 am, way too early and way too bright. Felt like garbage but managed to help Mark unload the Corvette off the trailer and walked the course, then slept a bit. This region likes to mix up the run-work order every event, so in June we worked 2nd heat and ran 4th (last), this time we ran 1st and worked 3rd.

    Mark offered another co-drive so we both entered in Super Street Mod (SSM) class again, which is where the car falls due to the relocation of the spring from the transverse to coilover location. Its not really a SSM car, not hardly, but its just "where it fits" and these events are just being used for some initial testing of the new shocks and springs. By 9 am we had the driver's meeting and then things got underway for Heat 1, when we were set to run.

    We planned a little better this time and had the "tire sprayer" loaded with water and ready in grid. The temperatures quickly climbed into the mid 90s and track temps were 145°F, as measured with an IR gun, so we needed the water this time. We lined up with the two-driver cars. I ran first, and that first run was a mess. Mark rode with me and we had a lot of wheelspin, but much of that was a dirty course - I was the 4th car to drive on it.

    We noted throughout the day that while the car would launch pretty hard from the standing start (3000 rpms) we still couldn't use 1st gear much, as the rear tires would start to break loose in a straight line at around 4500 rpms in that gear. So we short-shifted to 2nd at 4500 rpm every run and just used 2nd gear for the entire course. There were three VERY tight 180° turn-arounds and the revs were a bit low coming out of these, but it now has more torque and we didn't want to just shred the rear tires trying to use 1st - unlike the June TMS event at the same site, where we only had one run each before the thunderstorm hit, and both of our runs were terrible.

    This run group was a bit small and made the event rushed for us. After each run we barely had time to get the tires bled down, switch the numbers, reset the video cameras (one on roof, one mounted inside), spray the tires down (they were overheating badly, especially the left side), and then switch drivers and get belted in and the steering wheel back on. This left very little time to watch other cars, change the suspension settings, etc. In the end we only made a couple of small shock rebound changes, as the car seemed to be handling pretty dang well. The track was cleaning up and also getting hotter, and these outside changing variables kept us from doing any effective shock testing.

    Back in March at Optima, before the exhaust and tune, the car was "running out of gear" in 1st in the autocross, but 2nd was very sluggish because of the lack of mid-range torque. Looking at the before and after dyno charts, with the new exhaust and updated tune now, there is actually a 50 ft-lb increase in the mid-range, and it was noticeable at this event. Instead of trying to do the 1st-2nd-1st-2nd gear change dance, we could just leave the car in 2nd gear and let the low RPM torque pull us out of the 180° turns without feeling like the engine had no power.

    What was not working so well were the tire compound and brake booster. The 295/315 A6s Mark got for the June event were used scrubs, and there have been another 60 runs runs put on them since at the June TMS event, the June Oklahoma event with lots of runs, and this July TMS event with two drivers. Not only were the tires extremely HOT (after a run we couldn't touch them for a full second) they were heat cycled out. Dead, kaput, done. I am not a fan of doing testing on used tires, and then there's the fact that autocross competition events don't necessarily make for good tests. But its what we got, so be it.

    We both noted that the brake booster seemed to run out of assist after each short straight. I have noticed this before in our TT3 Mustang, running at this site back in May, where that car's booster was "running out of vacuum" after two long straights. I had to press so hard on the brake pedal then that I sheared the retaining pin that connected the brake pedal to the booster pushrod on that car. This same thing was happening to the C5 - either there is a vacuum leak in the booster or the big camshaft it has, with lots of overlap, is not producing enough vacuum after ~5 seconds of Wide Open Throttle. We were both overshooting the braking zone on the three 180° turn-arounds on our first two runs. On my third run I calmed down and just braked way early for each stop, which helped me drop two seconds and made for a 48.5 second run. I told Mark to try the same thing and he matched that time on his 4th run (48.6+1). By my 4th run I realized that these tires were blazing hot and weren't gripping like they should, so I slowed down all my inputs even more, which led to a 47.48 second run - the quickest time of the first heat.

    In-car Video of Terry's (first segment) then Mark's (second segment) best runs of the day.

    There's some video above that Mark shot with his GoPro of our best runs. Admittedly these runs don't look all that impressive, and at the end of the day the PAX placings weren't very good. Mark had cone trouble on his best run and seemed to be trying to use more steering angle than I was - and the tires just couldn't take it. It felt like we were on very heat-cycled tires, and that's what it boiled down to. I had to baby the throttle and temper the steering inputs or the tires would just run out of slip angle and slide. It felt a little like driving in the rain, to a degree - any abrupt input (brakes, steering, throttle) would over-tax the tires quickly. Driving here in May in my TT3 car on fresh 335/345 Hoosier A7s was a breeze - and had noticeably more grip!

    But still, even as low as the grip felt and the issue with the brake booster pushing our braking points back in the C5, that 47.4 run was 3rd quickest of the day (out of 134 cars) and the fastest of any "car with fenders". Our best time was only edged out by a tenth of a second in heat 3 by a shifter kart, and again in heat 4, when the surface was cleaner and rubbered in, by an FMod car. Would we have gone quicker in later heats? Mark maybe, but not me - lack of sleep was catching up to me, and I was glad to be done working after heat 3, to head home early!

    Jon (left) took CAM-C in his 2006 GT - also on MCS TT2s. The S550 (right) is looking quick in FStreet class

    It was a great event, a fun course, and well run as always. Thanks again to Mark for letting me co-drive and for doing the video, which saved me some time from my normal post-event routine of video editing. It was a fun day, even with the heat and from being pretty tired and dehydrated all day, I was glad to still be able to get some decent laps in. We took 1-2 in SSM against some more heavily prepped Corvettes, so that felt good as well.

    Before and After Cornering Images

    Its hard to convey how much better the car handles now than it did before, when it had the Konis and stock springs. One of the easiest ways to improve handling is to reduce roll, dive and heave by increasing spring rate - and when you do that, you can also lower the ride height for a lower center of gravity. Those go together - if you can compensate for shock lengths (like we did with the MCS set) and raise the rates enough to eliminate bottoming, a lower CG is a good trick to improve lateral grip all on its own.

    Based on a our experience we like to start off with at least least triple the front springs rates and double the rears on a 4 wheel independently suspended car like this one. As grip levels go up even more, so will the need for more spring rate. Of course when you increase spring rates dramatically you always need to improve the dampers to deal with that as well - and high quality monotube adjustables is the way to go. The Koni 3000s are technically monotube adjustables, but both the hassle and "randomness" of their infinitely adjustable valves is what makes them less than ideal, not to mention their excessive length leading to bottoming out the suspension when lowered. So the MCS is a good fit here. We could have used custom high rate transverse springs, and that would have been easier, but again - we like the low cost of coilover springs (Hyperco) vs $500/each custom built high rate transverse springs (Vette Brake Products).

    OK, no more theory, lets see some data. To me one of the best ways to show the handling improvement, outside of lap times or data logging on a fixed road course (we haven't gotten there yet on this car) is to look at images of the car loaded up in a high-g corner, which we have below.

    BEFORE: Koni Monotubes, stock springs, 295/315 BFG Rival street tires

    AFTER: MCS TT2s, Coilover spring upgrade, 295/315 Hoosier A6 R-compound tires

    As dramatic of a difference as these pictures show, it feels even MORE improved driving the car back to back. Mark didn't get to race the car on the old shocks/springs, but I did - and its a night and day difference. The new setup doesn't have the excessive roll and dive as the old, nor the "infinite spring rate spikes" when the shocks bottomed out, as they did before. This makes the car more precise at turn-in and gives the driver more confidence when pushing the car hard. Sure, the A6s were "compounded out" but it still had some decent grip and a good feel.

    The improvements are doubly impressive when you consider we have also upped the mechanical grip used with the MCS shocks. Going from (worn out) BFG Rivals to (worn out) Hoosier A6 tires, even in the same size, is a big step up in grip. But the C5 just seems to WANT MOAR GRIP! So we are working toward that next... new tires, and bigger tires.

    Having run probably 50 or more autocross events at this TMS site over the last 15 years, I feel like I can say with confidence that fresh Hoosiers in these same sizes would have been worth ~2 seconds that day, and on a hot day like this not having 2 drivers running back to back to back would have been a benefit as well. Moving up to wider tires like a 335/345 A7 would be worth even more. I cannot emphasize enough how important tires are in racing!

    continued below
    Last edited by Fair!; 07-21-2015, 12:37 PM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    continued from above

    Another big change to the set-up was going to real brake pads. I had so many problems with the Hawk HP+ pads on the front at Optima that those thankfully went away forever. We ordered him Carbotech XP20s for the front right now and we are looking at a Big Brake Kit from AP for his next round of mods. Mark rounded up some "gently used" Hoosier A6 tires in the similar sizes as the Rivals I ran before (295/30/18 front, 315/30/18 rear) and we mounted those to the same Forgestar CF5 18x11" wheels.

    Last but not least, Mark made a move away from his S197 Mustang and that helped fund the "Truck & Trailer Mod". His custom-ordered 18' dovetail steel deck twin axle trailer arrived the day before he had planned on picking up the car - good timing. We had to adjust all sorts of new things - ramps, straps, trailer hitch, load leveling bars, and placement of the car on the trailer - but we got it sorted and loaded the day before the Texas Region SCCA autocross at TMS Bus Lot.

    Last but not least, Jon made some class numbers and letters for the autocross event. As you can see he ran SSM class, which is more of an "anything goes" class for DOT legal R-compounds. My Sunday customer appointment got pushed at the last minute so I was able to co-drive with Mark at that event, and with 10 runs between us we could dial in the shocks and tire pressures on the whole new set-up. Mother Nature had other plans....

    Test Event - SCCA Autocross at TMS

    The event Sunday looked like it could be used for some decent testing of the new set-up of shocks, tires, brake pads and spring rates. Normally I don't like to make this many changes at once, but we knew they would all be beneficial to this car, based on the dismal performance at the Optima event. Who wouldn't take Hoosier A6 tires over worn out 200 treadwear streets? And Real brake pads over budget HP+ pads? And real monotube double adjustable shocks over Konis that bottom out when driving over a penny? And spring rates that firm up the car and remove lots of dive and roll? Here's a couple of pics of the C5 from Optima...

    Pictures of the C5 cornering at the March Optima event at TMS on street tires and stock springs. Note the front roll on the right pic

    I am a big proponent of using images of a car in various cornering states to help judge the setup of things like camber, spring rate, ride heights and more. Remember: the pictures above are with the Koni monotube adjustable dampers, stock springs, and pretty dead 200 treadwear tires. LOOK at how much roll there is, yikes.

    Picture Gallery: (not much there)

    So here in Texas we've had a LOT of rain this Spring and Summer. Enough that it made national news. But this weekend was scheduled to be clear and warm: 93°F and Sunny - that's a scorcher, so we brought a tire sprayer to deal with tire heat from a 2-driver car using Hoosiers on hot asphalt. This site has smooth sealed asphalt where you can see max lateral grip numbers of only about 1.3g on R-compounds.

    The course layout was not favorable to bigger cars like this Corvette - this was definitely more of a Miata/transient type course compared to the month before, where we set FTD and Top PAX in our 3600 pound TT3 Mustang (also running in the Street Mod category, below). But hey, you take what you can get when you are testing.

    I like this event site and we ran our TT3 Mustang here in May (above), where it did very well

    The sky was overcast when I woke up to leave for TMS, but I thought, "Meh, weatherman said no rain!" so I left my rain gear at home. Along with Mark - me, Brad and Jon from Vorshlag ran in this autocross event. There were 164 entries and 4 run heats, and we ended up having rain in 2 of the 4 heats. Jon, Mark and I got a bit unlucky and worked in heat 2 (where it rained) and ran in heat 4 (where it poured).

    Our shop manager Brad ran his STX prepped BMW 328is in the "X" class in heat three and had a bit more luck with the weather - this was the magic run heat that was dry, warm and fast. He has waited months on the RE71R (magic 200 TW tire) but they still weren't ready in his size, so he had to run on his old Hankook RS-3 tires, but still managed a respectable 3rd out of 10 in the "Pro class" (PAXed class for National level drivers, if they care to run it) and 8th out of 152 timed drivers in overall PAX. His wife Jen won the PAXed "W" class and also had fast run times, running in heat 2 in the wet/dry. They got dry runs on their 4th and 5th runs, where massive time dropped. I was announcing that heat and the 5th runs were pretty amazing, and virtually everyone got their best run by 2-3 seconds on their 5th.

    Heat 4 = 1 run then Thunderstorms

    The weather really screwed up the 4th run heat, though, with one dry run then.... BOOM! Massive thunderstorm with lightning that shut down the event. They refunded 50% of the entry fee for everyone in this heat - it was just hosed.

    Our order manager Jon ran his green 2006 Mustang GT in the 4th heat with us, taking the CAM-C win on his first and only run. Even with the win he was frustrated, as only having a single dry run ruins your PAX ranking and it's impossible to compare your time to someone in heat 1 or 3 that had five dry runs. It also ruins any testing you had planned.

    So Mark and I ran in heat 4 as well, and as one of only two 2-driver cars, we were first on the grid. The weather looked bad so I was happy to give Mark the first driver spot, and he took a wild and wooly first run, all in first gear. I wish the camera worked - it was all sideways. I rode along with him (it's allowed here) and we were laughing as he slipped and slid his way around the track. The shock settings were wrong, the tire pressures were too high, but he had fun and we could feel the used R-compound tires start to come in as he scrubbed off some rubber. We lowered the pressures then made some small shock changes, but knew we'd be making more changes soon. It was LOOSE.

    The "Best" pics I got of the C5 loaded in a corner. Flatter by a significant amount

    I slotted in next, and realized I was a bit close to the steering wheel. Oh well, no adjustments possible without unbolting the seat, so I just drove it. We had bled the tires down to 30-32 psi, they were nice and warm, and the ground was still dry. It had been about 6 hours since we walked the course, though, and I was having trouble remembering the layout - which worked it's way around and inside itself a bit. Mark rode through with me and we talked a bit during this run...

    terrible driving in this lone run we got on film in the dry

    Before you get started with the comments, yes, this run is terrible. I probably should not even show it, as it makes me look like more of a awful driver than I really am. But it was my first and only dry run, so just ignore the over-driving, topping out 1st gear 4 times, and ugly hand use. The car was set WAY loose and a handful to point in the right direction, and the gearing was between 1st and 2nd. By the end of this run you can hear us talking about shifting earlier and doing the whole course in 2nd gear instead of mostly in 1st, like this one. I also tend to calm down a lot when I have a clean time in the books (surprisingly, this run was cone-free).

    I only show this video because it's the only dry run we got on film. :/ The thunderstorms rolled in after 1st runs and it was all over. I took one run in the rain and was hydroplaning all over the place and fully 16 seconds slower. Then they shut the event down because of nearby lightning strikes.


    I shouldn't even post the results, because with one run they are meaningless. But I wanted to point out one thing - as bad as that run was, as badly as it was driven, as far from the correct damper set-up it was at - this run time was one of the quickest for first runs, for all drivers in all heats. We were on our way to a good result, and my "butt dyno" felt a 43 second time in the car. Again - it looked bad on video, and it was pretty bad driving, but the car was still pretty fast. That's all that matters here: the car has a lot of potential, and it's not even being built to autocross.

    After my hilarious slip-n-slide pouring rain run #2, the lightning started and hit close by - across the street - and they sent the corner workers and everyone in grid to find shelter. We camped out in a buddy's truck and waited for the lightning to pass, then I helped pick up the course while Mark loaded his car on the trailer, in the rain. Absolutely not the test we had imagined, but what can you do?

    OKC SCCA Autocross Testing June 28, 2015

    Mark took the C5 to an autocross event (yesterday) in Oklahoma where he had 8 runs to dial the car in. Results are posted, but Mark wanted to let me know that he was testing yet took passengers on all of his runs. He had a cone on his fastest run at the starting line, which the side exhaust blew over, LOL! Hey, we were told this was to be a track car, so I can't worry about cone sneezes.

    If you ignore the "exhaust breeze" cone he had the 4th quickest time of the day, and was still dialing in the car (double adjustable shocks). He is going to come back down July 12th for the Texas Region SCCA autocross event where we will both drive the car again and do some more setup work. Then he has a Hallett test day for Sept 2nd to work on some times on a road course, finally.

    What's Next?

    Mark was still happy with the car, as even with only a single dry run he could feel the improvements. The brakes actually worked now that the street Hawk pads were removed. We drove around city streets in the car on Saturday and the ride quality was firm but not unreasonable with the 650F/700R rates, and never bottomed out - even going over some rough railroad crossings. The car cornered flatter and had no noticeable brake dive like before. The sound of the exhaust was both pleasing and much quieter than before. The new engine tune was easier to drive (no more stalling at idle) and the power delivery was much smoother than before.

    All of the mods from Round 1 (basic repairs + 18x11 wheels and Rivals) and Round 2 (shocks, springs, engine tune, exhaust, Hoosiers) made for dramatic improvements, but more testing is needed to dial in the shocks. Mark could finally take his car back home to Oklahoma and he will be hitting some track events at Hallett (his home track, which is one of my favorites) and some autocrosses in his SCCA region (he has already done one more autocross).

    We have Round 3 of mods planned with Mark, and they are extensive. These include Safety upgrades (roll bar, HANS, fire bottle, main power kill switch), Brakes (AP brakes front and rear + Ducting), Drivetrain (Gearing, LSD, Accusump, Oil Cooler), and Aero improvements (wing, splitter, more). Once these are tackled it should be a pretty quick TT2 car, but when he gets some lap times at Hallett with the current setup posted I will share them here. The previous owner had some quick 1:24 laps there on Hoosiers with the old Koni/TTA setup, and we shall see if we've made it better or not pretty soon. Since we had my TT3 setup in the 1:21s at Hallett I'm pretty sure we can go faster with a 600 pound lighter C5 Corvette setup for TT2?

    That's all for this time - Thanks for reading!
    Last edited by Fair!; 06-29-2015, 03:55 PM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    continued from above

    We had done the same type of rear upper shock mount on a C5 Corvette many years ago (it never went into production), but this time we refined it by adding easier access to the top knob from the rear hatch area. It's a simple upper mount using our oversized 3/4" spherical bearing with two thru-bolt holes that attach the flange of the assembly into existing threaded factory holes in the rear. Note: the access hole for the upper knob in the rear fiberglass recently became legal for many SCCA folks, see 13.5.F, but converting from leaf to coilover is not legal for Street, Street Prepared or Street Touring classes. It's fine for Street Mod or NASA TT1/2/3, though.

    The new Vorshlag spherical top mounts are shown at the rear (left) and the front (right) shock locations.

    We left the factory lower rubber shock bushing on the bottom in place for now, but there are off the shelf conversion kits to make this into a spherical bearing also (maybe we will do this on Round 3 of mods). The front MCS shocks lower bushing is already a spherical, as part of their T-bar lower mount.

    The front upper shock mount was something a bit more unusual, done differently than the other coilover setups on these cars. Most of the spherical upper shock mounts we've seen for C5/C6 coilover front shocks are really just "eye" upper shocks with an adapter to bolt to the stock pin mount hole. That makes for a tall ding-dong looking device sitting above the shock, and the spherical bearing is way below the factory mounting hole - which eats up a lot of front shock stroke (but gains room for the coilover spring to the upper control arm). Our set-up is unique in that the spherical bearing is slightly above the factory upper shock mounting hole - which gains additional shock stroke. We offset and enlarged the factory upper mounting hole inboard, which is how we gain room for the spring clearance needed relative to the upper control arm. It will make sense when we publish the production pictures + instructions.

    The face of the spherical bearing mount still has plenty of surface area - more so than the factory rubber bushings did - and can pass the loads into the whole upper shock mounting structure, which is thick multi-layer steel assembly welded to the frame of the chassis. Doing this offset upper hole moves the top of the shock inboard, which gained room for the newly added coilover spring. We also went with 2.25" ID vs larger 60mm ID coilover springs for more clearance to the control arm.

    Common coilover spring diameter sizes are 1.75", 2", 2.25", 60mm, 2.5", and 70 mm - which are listed from smallest to largest

    It sounds complicated but was actually quite easy. Again, this atypical spherical mount setup removed a rubber bushing from the suspension load path plus gave us MORE BUMP TRAVEL, both good things. Spherical bearings pivot smoothly and can carry a LOT of impact load, unlike rubber which can bind in pivot and crush in compression.

    The spring rates we chose were a compromise - like everything on any race car, or any race/street car. Mark has since bought a trailer and decided to make this a more dedicated race car, but... he wants to hang onto some street manners for a while longer - like catalysts, interior and air conditioning - so we had a tough call to make on picking the rates. He was also stepping up from 200 treadwear tires to Hoosier A6 tires, which he told us the week we were installing these coilovers.

    Jason wanted super stiff and I wanted just moderately stiff, so we argued, calculated, and finally settled on 650 front and 700 rear rates in 2.25" diameter and specific lengths that would fit the confines of the suspension. This is about triple the front spring rate and about double the rear of the OEM transverse springs - we think. You see, there are a couple of ways people measure the spring rates on the transverse factory parts and nobody seems to have real a good, definitive listing of C5 springs' actual "wheel rates" (spring rate at the wheel, with motion ratios and funky spring shapes taken out of the equation). The measurement styles or conflicting spring rate data doesn't really matter - all that we care about is how the springs and dampers perform.

    Luckily we had a test event scheduled with Mark the next weekend, which we could use to dial in some of the settings, so we worked overtime to get it all together before he came by to load up with his new trailer on Saturday.

    Making Spherical Bearing Shock Mounts

    Some folks like watching the step-by-step images we show on social media of new parts as they are developed and built. Here's a few steps of the making of these C5/C6 Corvette upper shock mounts, which happened over the course of 2 days (from design, to a brand new machined part, to on the car and driving).

    First step is always measurements from a car. The C5 was lifted up on one side and the stock shocks were removed. We test fit the shocks and several springs a few times and saw all of the tight spots. Some measurements and tracings of OEM panels were made, an initial design concept was made for both ends, which Jason and I reviewed together, tweaked, and then he made into a final design in CAD. Then the material was ordered...

    By the time the two billets of aluminum alloy arrived, the CAM design was programmed and ready for the CNC machine. Specific length slugs were cut on our coolant-fed band saw and loaded into outer jaws in the CNC lathe.

    The front and rear slugs were machined on one side, then custom soft jaws were installed and machined to grab the "tower" of the rough machined parts. Then the ID was machined to accept the press-fit spherical bearings, with several high tolerance dimensions. This was the first two "ops", completed all on the lathe.

    The finish machined "rounds" were then ready for the CNC mill, to cut the perimeters of the mounting faces that attach to the chassis. To do this required three fixtures - one to hold the tower shape on op 3, and another two to hold the bases for op 4 on the mill. Lots of programming and setup but very little machine time. We made 8 pieces and only needed 4, and didn't anodize them but left them in raw aluminum - typical of a prototype part. Mark is a tester and knows all of this going into the build.

    The spherical bearings were test-fit into the rounds to verify the dimensions and fit before they went into the mill, of course. We actually skipped op 4 (just a chamfer on the top edges of the base flange) since they were only for cosmetics and would be covered up once installed. The production pieces will get op 4, of course, along with a red anodized coating.

    All told about 25 man hours were spent measuring, designing, programming, machining and test fitting these parts, all of which we eat in the name of R&D. Testing should prove the parts work (or need a tweek) and we would have another successful product that we can sell for years to come. We shall see...

    That's a good visualization of the starting billet and the finished parts. Lots of steps taken to get from round bar to final product, and hopefully you enjoyed the little step-by-step here.

    Additional Mods

    Mark has a lot of future plans for this car but wanted a quick release race steering wheel to complete Round 2 of mods complete. We put together an estimate for his requested racing steering wheel and quick release and got he parts coming when he approved the choices, colors and numbers.

    We suggested the models of the wheel and quick release ultimately chosen, using brands and models we have used in the past. The steering wheel is a MOMO model 88 in 350mm diameter (also available in 320mm) with a black suede covering and flat bottom design. I've used this wheel on four of my own race cars in the past and numerous customer cars. The GM hub adapter is a MOMO piece, which goes to a 70mm diameter 6-bolt circle common to Sparco, MOMO, OMP and other racing steering wheel makers. The quick release hub is from Lifeline, who also makes the Sparco branded part that looks identical. We've used all of these parts before, and sell these to racers all the time. The QR comes in gold and black, and Mark picked gold.

    We have used a lot of different steering wheel Quick Release hubs over the years. My only advice is this: while there is a big price difference between the circle track QR hubs, Chinese/eBay QR hubs, and the high end hubs like this Lifeline/Sparco unit, there is an even bigger difference in feel and "slop" between the low priced and high priced units. This is another one of these "you get what you pay for" deals, all the way.

    These parts are often finicky to install and took some special care to get the factory airbag out, remove the OEM steering wheel, fit the MOMO hub adapter, and trim the column surround plastics. The QR hub and MOMO wheel were the easiest bits to install. One thing to remember is that a QR hub always adds depth to the column, pushing the steering wheel about 2" closer to the driver.

    This worked out perfectly for Mark yet when I drove the car (with a fixed seat placement) it put the wheel a bit close to my chest - but this car isn't built for me, it's built for Mark! And this car, fitted with high side bolster 1-piece racing seats, removing the steering wheel does make it easier to get in and out of. And the new wheel... mmm, it feels so nice. Good stuff.

    continued below

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    Project Update for June 29th, 2015: We've been working on Mark's C5 Corvette since the Optima event and have made big strides. We have some new products we're testing on this car which are somewhat significant, too. Mark finally got to race this car at an autocross, where I co-drove with him. This was to be a test of the new set-up, but we had some weather issues, which I will detail below. Let's get caught up.

    Unintended Weight Loss

    If you have ever read one of my posts you know I'm a freak for weights... we tend to weigh cars and parts more than other shops, because we know how important weight is in racing. After tires, weight matters most. So let's look at what we started with...

    Left: The weight of Mark's C5 after Round 1 of mods (3114); Right: Weight of a stock C7 Z06 for comparison (3570)

    The 3114 pound weight above was after Round 1 of mods were added - it had almost no fuel, full length headers (lighter than cast iron manifolds), 18x11" Forgestar wheels (the 18x10.5" TSW wheels it started with were even heavier), two composite Sparco race seats, harness bar, and a Borla exhaust. That's not bad, considering what a stock, carbon fiber C7 Z06 Corvette weighs (3570 lbs) - which is about the same as a 4 seat 2011-14 Mustang GT with a giant DOHC V8, stick axle and steel bodywork. Mark came from a 2012 Mustang GT before this car.

    We haven't really done any real weight saving tricks on this C5 in Round 2 of the mods, just component upgrades to make it faster. But we always keep an eye on weights and pick parts that are "weight neutral" or lighter, whenever we can.

    And this picture above is where we are now, with similar fuel levels (almost none), which is 3050 pounds. This is almost exactly what a C5 Z06 weighs (I've weighed one at 3048 lbs, which was stock and low fuel). The Z06 is a lighter car than a coupe from the factory, as it doesn't have the giant glass rear hatch, no removable roof, narrower wheels than this car has, and a titanium exhaust. And while a 64 pound loss might not seem like a big deal, we weren't even trying to remove weight here. The car still has full interior, air conditioning, and we even went with heavier front rotors (Centric 1-piece vs Stoptech 2-piece). So a semi-stripped C5 Coupe could easily get under 2900 pounds or less.

    A Brief Detour To Talk About Time Trial

    This new weight of 3050 + a 200 pound driver with the new 425 whp power number (up from 400) puts power to weight at 7.64:1 (down from 8.4:1 when it got to us), which is a tick better than TT2 territory (8.0:1). This is good - so with a little ballast or bit less power it could get right at limit of the TT2 class, when Mark takes the TT plunge. Sometimes it is tough to fit in one of the three numbered TT classes (TT1/2/3), but this one works out perfectly.

    Does this TT and power-to-weight ratio stuff sound confusing? I talk a bit more about TT classes in this thread on the S197forums. Yes, this is a Mustang forum, but the sub-section (corner carvers) where we read and post there is pretty focused, and we have had some decent tech discussions there. In post #23 there I talk about the pros and cons of autocross vs HPDE vs Time Trial vs W2W racing. Posts #28 and #33 is where I talk a bit more about Time Trial, which Mark is building this C5 for.

    Time Trial rules might seem confusing at first glance by racers from other racing groups or non-racers, but it's really quite simple: measured wheel horsepower and measured weights (with driver) are combined to form a ratio (power to weight). This is the CORE basis for almost all NASA racing (W2W) and TT classes. It works really well - better than "engine displacement to weight" ratios and "turbo modifiers" that the SCCA likes to use (which was dropped in the 1970s by almost every other racing organization on the planet). Let's look at some numbers...

    Relative Ranking of NASA Classes
    TT1 5.50:1
    TT2 8.00:1
    TT3 (stock aero ) 9.00:1
    TT3 (modified aero) 9.4:1
    American Iron 9.0:1 to 9.5:1
    TTB 10.50:1
    Spec Iron 11.75:1
    TTC 12.00:1
    CMC ~12.7:1
    TTD 14.25:1
    TTE 16.50:1
    TTF 19.50:1

    AI, SI and CMC are three popular "pony car" wheel to wheel (W2W) racing classes within NASA, in case you are unfamiliar with those names. There are small power-to-weight modifiers to all of these classes, especially the numbered classes, but these base numbers are pretty much the goal you shoot for. Not all "letter class" TT cars can hit the power to weight max (with the limitations on mods, you are lucky if you can!) but the number class cars can (its just costs money!).

    I ran our TT3 Mustang at 8.8:1, even with the -0.4 "non-stock aero" hit (we picked up an even bigger ratio bonus for running over 3801 pounds, +0.6). We run our TTC Corvette at 11.3:1 with a bonus for only running a 245mm tire (+0.7). And when it comes to the modifiers, "minus equals plus and plus equals minus"... I know, it's wack, just don't ask.

    Suspension Development + Hoosiers

    During the past 7 or so weeks since Optima we have done a bit of development. Lex from MCS stopped by our shop and we discussed shock options for the C5, as well as the two big spring choices - monoleaf vs coilover springs.

    The C5 uses a single transverse mounted monoleaf spring at both the front and rear of the chassis, of course, and the Y-body Corvette chassis has done this for generations. Mark's base C5 Coupe was fitted with the two springs above. There is some associated hardware that goes with mounting the monoleafs, which we removed, shown below.

    We swapped the C5's factory transverse springs for a quartet of 2.25" diameter steel coilover springs from Hyperco, which I have weighed above, top right. So if you add up the monoleaf spring and hardware weights (9.7 + 11.9 + 3.6) that's 25.2 pounds, replaced by 8.6 pounds of coilover springs. Now we didn't weigh the MCS TT2 aluminum bodied monotubes, but they are probably another 4-5 pounds lighter on each corner than the steel bodied Konis that came off (which are already sold). So a good bit of the weight loss in Round 2 came from the suspension changes, the rest was in the exhaust and airbag delete + race steering wheel.

    Coilover springs (left) are more common, cheaper and come in more rate options than monoleaf springs (right), which are built to order

    And yes, we could have used custom built, higher rate monoleaf springs (see above right) instead of coilover springs, and that's what we did on our C4 Corvette for TTC. For the C5 we could have sourced monoleaf springs from the same place as these coilover springs - Hyperco. Why didn't we? Three reasons - cost, availability/options, and time to change springs track side.

    Lex summed it up best: "You can take a dozen coilover springs with you to test at the track - easy to change, cheap to buy, tons of rate and length options. Are you going to buy an equal number of ($500/each) monoleaf springs to test with?" He has a point. At $80-100 each for Hyperco coilover springs, this gives you a lot more flexibility and options to test with, plus they are a lot easier to change track side. Plus they are lighter and don't have any "unintended swaybar effect" like transverse monoleaf springs do.

    After deciding on using coilover springs (which moves the load path of the suspension from the leaf mounts to the shock mounts) we knew we wanted to make some spherical shock mounts for this chassis different than what other companies have made. With these two pieces of info we ordered the MCS TT2 shocks (above) in different lengths and configurations than normal. We definitely didn't want to end up with dampers that were "too long", like the set that came off this car.

    The comparisons above show the front shocks (left) and rear shocks (right), Koni 3000 series vs MCS TT2. The new fronts are shorter and have a little more bump travel. Couple that with our raised height spherical mounts and they had even more travel. The rear was the nightmare with the Koni's, and with ride heights 1/2" lower than stock we were left with only 1/4" of bump travel. That ain't enough. The new MCS body length is slightly shorter, and non-inverted. But the big space savings was moving the adjuster to the top of the shaft instead of the one built into the lower fork. That saves almost 3/4" of an inch in body length alone, which equals more stroke in the bump direction. After you look at the motion ratio of the shock it makes for about 2 inches more bump travel = plenty.

    Here's a close-up of the inverted front MCS monotube double adjustable, which we call the "TT2" shock series (TT1 = single adjustable non-remotes). Like I said, we didn't have the rear shock inverted to save room, but left the fronts inverted (how they normally make them for a C5/C6). That means the rear shocks' 2-stage adjuster knob would be buried inside the "blind hole" that the factory shocks mount into.

    So we cut a big hole above the shock to gain access to the knob. This was a relatively easy fix, and makes for MUCH easier shock adjustments than before with the Konis (jack up car, insert tool, rotate and hope to make both sides the same). Now the knobs can be reached quickly - pop the rear hatch, lift the carpet, and turn the knob. Pull up for compression, push down for rebound, nice positive clicks.

    The C5's rear TT2 shocks us the traditional MCS 2-way knob, shown in the video above - down for Rebound, up for Compression

    The trunk access holes above were made by first removing the rear shocks, looking at the blind hole, then approximating the center of this hole and drilling a 1/8" pilot hole up through the fiberglass rear deck. Once the center of the shock opening was located by this pilot hole, a 2" hole saw (with an 1/8" pilot drill) was used to cut the openings from the top side. We cleaned them up after these pics were taken and temporally stuffed a foam koozie down inside the cavity through this 2" opening, to make a water tight seal around the shock shaft. There is nothing really structural here, and the pilot hole kept the 2" hole saw centered over the blind shock cavity and away from the steel frame rail. We will install a better cover next time the car is at our shop.

    The upper shock mount itself is something we designed and machined in-house, to test on Mark's car. This eliminates a big "double rubber bushing" mount in the upper part of the shock, which becomes more crucial when you move the suspension loads to the shock mounts (which only see "damper loads" in stock form).

    continued below
    Last edited by Fair!; 06-29-2015, 03:32 PM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    continued from above

    After making that video, I've learned a lot more about this particular car. It was built for a certain class where some of the parts sort of make sense. Some parts on this car aren't as terrible when used in "ideal conditions" - the shocks might work fine on a smooth track and at stock ride height, and the other parts fit this points based letter class in NASA (TTA). So now the choices make more sense to me: using these aftermarket shocks but not upgrading the springs (more points), doing the headers and other exhaust bits (used to be +5), cold air (+1), and the BIG cam upgrade (+6) to get to a target power number. It probably stacked up well against the old C5 Z06 entries that used to rule TTA class. The part selection was also partially budget driven, and that's OK.

    Left: Up through the 2012 season, TTA class was alive and well. Right: By 2013 TTA was dead and TT3 was a whole new ballgame.

    The previous owner raced this car in NASA's TTA class at Hallett from 2010-12, and did fairly well in the car. The lap times (1:24s) were pretty good and he won plenty of contingency tires. TTA was a popular and competitive class that had a LOT of variety, but the C5 Z06 pretty much dominated at the top levels there for years. There are loads of posts about the loss of this class, but by 2012 it was dead and not coming back.

    Since 2013, all C5 Corvettes go straight into TT1/2/3, so "points" mods restrictions are no longer a driving factor in parts selection. Instead of picking selective mods around a class that no longer exists, living with big compromises on the street, and being stuck with stock ride heights, the new owner Mark is going to build it with a bigger budget and NASA TT2 class in mind. So again, sorry if I was too harsh in my video above, and I kind of get it now, but there were still some big compromises to the set-up.

    My "8 minute bitchfest" video also showed some of the driveability items that were above and beyond the problems uncovered during competition at Optima, which included:
    • A glitch which kept the car from running properly or having enough power to exceed about 60 mph with the factory Traction Control turned on (I figured that out the morning we went to TMS, within 5 minutes of driving the car for the first time on the highway)
    • The loud droning of the Borla exhaust was ear splitting at highway speeds
    • The rough tune wouldn't idle or cruise under 1500 rpms; you had to use a lower gear to keep the revs up or it bucked and stumbled, which made the drone even worse
    • The ride quality on the long-ish Konis suffered on the street - any real bumps would bottom the rear shocks, sending the spring rate to infinite
    • The clutch engagement was not smooth and made stop-and-go traffic a hassle. The lack of idle made the engine die when stopped, so you had to drive with 3 feet.

    Long story short, it was a chore to street drive, which was a big ask for only 400 whp. Something wasn't right, and I knew our friends at True Street Motorsports could work their magic and tune out these driveability issues. But first, we needed to so something about this exhaust before they retuned the motor.

    What's Next for the eBay Corvette? UPGRADES!

    So after we finally had a few days to catch up after Optima in March we spoke with Mark and he even come by the shop to talk to us in person about plans. The general consensus was that there were several issues we found at Optima that needed to be rectified, and he had some choices to make regarding the suspension, exhaust, engine tune, and brakes. We also needed to know what color to powder coat the Forgestar CF5 wheels, since we had to rush order the set "raw" to make them in time for Optima.

    So let's get to the fun part of this post - the upgrades! First, here's the former dyno graph from the previous tune done when the cam was added.

    Yes, the image is hard to read but the basic numbers are: 338 whp / 356 wtq before the cam, and 400 whp / 381 wtq after the mega-cam and a tune were added. Big add for the cam, obviously, but it came at a cost of smoothness, idle, and other issues. From what I am told this power level was how the car was purchased by Mark this Spring. Something wonky happened to the tune after this old dyno chart was made, as I've had LG tune our cars in the past and they did a great job. Who knows, but whatever the reason, it ran like crap when Mark received it.

    New Axle-Back Exhaust

    The first item we all agreed needed to change was the exhaust. It was too loud and after looking at it up close, I felt it was also restrictive. The weird routing and tubing sizes looked all wrong to me. Did I mention that the tiny Borla mufflers + full length headers made the car EAR SPLITTINGLY LOUD? Yea, it was unpleasant, and I noted as much in the in-car video - where you can barely hear me describe the issues with the car over the monotonous exhaust DRONE.

    I've built a lot of custom exhaust systems and installed dozens of off-the-shelf performance exhaust systems over the past 28 years of being a hobbyist fabricator/racer, a mechanic at a tuner shop, and then the owner at Vorshlag for the past decade. We have two really good fabricators here (Ryan and Olof) and two engineers that understand flow (Jason and I) and exhaust sound. We are also fanatics for lower weight, higher quality materials, and adding simplicity when possible.

    The Borla axle-back system above isn't great, but it isn't 100% terrible. This C5 already had that installed, plus some nondescript long tube headers, all of which is just rusty enough to be recognized as 409 stainless. The header collectors, cats and mid-pipe section are 2.75" OD but the Borla axle-back section is only 2.5" OD. We know how to measure pipe and have a dozen calipers around the shop, so you're gonna have to trust me on those numbers.

    The routing that the OEM system, this Borla system, and seemingly ALL aftermarket exhaust systems seem to take on a C5 is torturous and needlessly compromised. Its ALL ABOUT THE QUAD CHROME TIPS, yo. There are lots of bends and not a lot of room for a properly sized muffler case. And in the case of exhaust tubing and muffler case, bigger IS better.

    We've done lots of before/after measured sound tests and lots of before/after dyno tests and after years of doing that we have figured out what works and what doesn't matter. When excessive NOISE is a problem we found that a LARGER case muffler of a certain type knocks the sound levels down. DRONE is handled in another way, and PERFORMANCE is all about maintaining a smooth and larger inner diameter and minimizing bends. So we spec'd out the biggest Magnaflow 304 stainless mufflers we could fit in the rear and got those coming, plus a lot of 3" mandrel bent tubing and some real stainless V-band clamp assemblies.

    My new routing idea was fairly simple but not something we'd seen before on a C5 - exit out the side. This let us avoid a pair of 180° bends and a pair of 90° bends as well. This also gave us more ROOM for a bigger muffler case. This isn't revolutionary and since we built this I've had people show me other examples of this routing on C5/C6 Corvettes. Not surprising - its the only routing that makes sense.

    Exhaust leaks are also a pet peeve of mine, and I find any audible leaks unacceptable. There's a half dozen ways to make a multi-piece exhaust system join together, and the "common" ways are the cheaper, most leak prone joint types: slip-fit and ball-and-socket joints are the worst, with bolted flanges with gaskets coming a close second. The proper way we've found, which is the most costly and complicated to install, is a V-band flange connection. Done right, these never leak.

    We also build exhausts to be lighter, and can often save 40-80 pounds over OEM systems. But this car didn't have the stock exhaust, so we didn't weigh the changes. Since I also hate rusty exhaust components, we always stick with 304 stainless steel exclusively. Titanium is a real bear to weld and EXPENSIVE, and the less dense material makes for more noise. So we keep a lot of mandrel bent 2.5" and 3" 304SS tubing around.

    Like all race shops would build it, we piece the systems together from the mandrel bends - slicing, fitting and tacking them together as we go. After tacked we remove the finished assembly and final welding everything on the fab bench. This is the right way to do one-off exhaust systems, but its time consuming and the materials are expensive. Spending 12-20 hours building an exhaust is not unheard of, and at our current shop rate ($105/hour) it can add up. This isn't the right choice for many folks, but when the options are all compromised (like the C5) or its a custom race exhaust where every ounce matters, or you need a quieter set-up than the aftermarket offers - this way works. And we stay pretty dang busy.

    Not shown well is the layers of heat shielding we added on the inside of the rear "fenders" (bumper cover). This includes a composite aluminum/fiberglass mat on the inside surface with DEI gold foil reflective barrier on the top of that, near the muffler case.

    The outside of the body has hand formed (to match the curve of the body) 304SS heat shields shown above, bolted in place with stainless button head M6 bolts. The exhaust system "grows" (front to back and laterally) when it gets hot, so there's a necessary gap around the tail pipes that changes slightly with temperature. If the stainless plates get covered in soot they can be hit lightly with steel wool and be shiny again.

    The new sound (see video below) is a lot more pleasing, still having a bark on the outside but MUCH quieter inside. Oh, and this change along with a re-tune gained 25 whp...

    Sean at True Street dyno tuned it this week and as you can see (above) it now makes 425 whp and 398 wtq. Not spectacular, but its still just a stock 5.7L LS1 with a cam, headers and a cold air. It picked up 25 whp and 23 wtq from the exhaust changes and their conservative "road course" dyno tune (STD corrections). We had them tune it for 91 octane (the best at most Oklahoma gas stations where Mark lines) and for road course use, so this isn't some ragged edge drag race tune, either. In a 3100 pound C5 with 425 whp it goes plenty well, and it would put the car near the limit for NASA TT2 as it sits... (nominally an 8:1 power to weight ratio class, with driver on board).

    Click for video (tested on a closed course in Mexico):

    Why has nobody made a C5 exhaust system "kit" like this? It isn't easy to install nor replicate for an off-the-shelf system that is easy for a DIY installer to put on these cars. There's cutting of the bodywork and the V-band clamps don't have any "slop" to allow for alignment. It was made to fit THIS car. People have already asked me what it would cost to build an axle-back set-up like this and ship it to them, and I said "first, ship me your car". This is a custom exhaust set-up that we have to fit to a given car. Not only are the large diameter tubes tough to fit around things like transaxle, suspension and halfshafts, the exhaust outlets need the heat shielding inside and out.

    Wheels Get Color

    The color Mark went with is a Blood Red powder coat that we had done at a local powder coat shop we've worked with for years. Yes, it was baked under 400°F, yes it is safe, and yes virtually all wheels you can buy are powder coated. Please don't chime in with your internet stories of cracked wheels from powder coating. That was a scare from the 1990s and any decent powder coat shop knows how to coat aluminum wheels without altering the temper. Please don't propagate old internet wives tales, thanks.

    Anyway, the finish came out beautifully and the pop of color really helps this otherwise bland silver Corvette.

    NEXT: Suspension Plans

    We have spec'd some MCS TT2 dampers for the car, which are being built and should arrive soon. We will install these with some other parts we want to make, which I will discuss in the next post. We will be removing the transverse springs in the process and go to coilover springs. Why go to that trouble? Why not spec a custom VBP transverse spring for both ends? Well we almost did that, and had really good results from the 1170 pound VBP (above left) custom front spring on my TTC prepped C4 Corvette.

    After talking with Lex from MCS about this car when he was at our shop recently, he made a simple point: how can you tune the spring rates at the track if you only have $500/each transverse springs? A coilover spring is a whole lot easier to change and a lot cheaper to test several rates with. We can carry a dozen springs to the track and let the clocks show us what works best. Good idea.

    Moving the springs to the shock (coilover) and away from the OEM mounting locations is no trivial matter on this car, though. You are essentially moving all SPRING loads onto places on the chassis and control arms that were designed for DAMPER loads. So things will be altered and beefed up to hold these higher loads. We will share more next time...

    What's Next?

    We have done a lot of events since Optima in our other cars, but the next event scheduled for the C5 is below:
    • May 30th - Five Star Ford @ ECR (HPDE event)

    Originally scheduled for May 9th but was moved due to heavy storms, which gives us time to knock out some work on the C5. This time Mark can make it down to drive the car on proper dampers that don't bottom out after 1/4" of travel. He will never know the joys I had at Optima!

    We're also working on a number of other interesting projects...

    This Week at Vorshlag video for May 8, 2015

    Click above our my latest "This Week at Vorshlag" video, linked here. In that I cover many of the other projects going on in our shop that week, so watch that or check out our Facebook page or Blog to see what we're working on outside of the Mustang world. I write insanely detailed forum build threads for all sorts of other car chassis and types...

    Thanks for reading!
    Last edited by Fair!; 05-20-2015, 09:20 AM.

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  • Fair!
    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

    continued from above

    I was frustrated with the C5, physically tired, and the car now needed a major bath. So did I. But somehow, even with all my complaining and car troubles, this event was still a TON of fun. All of these frustrations were my own damned fault - for bringing a completely untested car with questionable parts to a televised event before we had a chance to fix the many wrongs done to it. Amy also had a struggle in the Mustang, driving in events she had never done, a course she had never driven, and on tires and an aero set-up she was very unfamiliar with. But she and I had several on camera interviews, we met a lot of cool folks, and got to see a lot of kick ass cars. The Optima/USCA folks took care of everyone and made sure we were having fun.

    Unlike some previous USCA/Optima events, they were very good about posting times up during the event, even had live timing up on Sunday, all of which was a welcome change. Since my driving felt so terrible I had no illusions of placing well in class. Of course there were still some surprises at the results ceremony at the end of Sunday.

    Wow, these cellphone pics have major #potatocam filter going!

    As I mentioned above, Amy's Mustang finished 2nd in the Design and Engineering competition against one of Ken Thwaits' two entries and our customer James Meeker got 3rd - both cars have been featured in this S197 build thread many times (we have Meeker's car in our shop now for more cool updates, which I will share next time).

    As you can see in the results above, James did well at the Hot Lap track event, (using the MCS RR2 doubles + Vorshlag camber plates + Whiteline everything + 18x11 Forgestars) taking 6th place right behind Aaron Sockwell's 2015 GT (which has MCS TT2 shocks and Vorshlag camber plates + 18x11 Forgestars). As I mentioned before, Aaron's 2015 looked good out there and we weren't surprised when he took 5th in the Hot Lap event (somehow a 2 seater 2006 Corvette snuck into the GT class to take 3rd?) and 3rd overall in GT class. Amy, Doug, Jon and even Shannon were all in the hunt on the road course, too.

    Matteucci's 2nd place Autocross and Speed Stop times were good enough to put him into 2nd overall out of 12 in GTS class, fighting against the lightest and fastest cars at this event - in a stock C5 Z06 with a worn out motor (this was the last event he ran in this car before pulling the tired LS6). Ronnie Soliman took 1st in the Autocross, Speed Stop and Hot Lap challenge in his 2006 Evo, which was very light and well built. Those AWD cars are still the overdog cars to watch out for in GTS - and since they combine all the classes for the main OUSCI event, also a threat to win it all in Las Vegas. If I were a betting man that's what I'd pick for the finale after SEMA.

    As bad as it felt, somehow the eBay Corvette earned 3rd overall in GTS class, surrounded again by AWD buggies. This was a complete shock to me, as I felt like my Speed Stop times and Design/Engineering score would keep me off the podium. But hey, I'll take 3rd in this mess of a car. Just going .04 seconds quicker in the Speed Stop would have put me in 2nd place in GTS class, but I was a long way from 1st. That was taken by our friend Todd Earsly in his EVO. Todd made a concentrated effort to focus on Optima events about a year ago, running NASA events in TT1 class on street tires just for the practice, and its really paying off - this GTS class win gets him a spot in the 2015 OUSCI event. Congrats to him!

    The Optima folks worked hard all weekend to keep everything running smoothly, and I'm happy to report that they did a nearly perfect job. Well worth the time and entry fee, so if you see one of their events coming to a road course near you, GO AND ENTER. As Matteucci showed, a stock car on decent tires can still do as well (2nd place with a busted motor) in even the toughest classes, if you can drive well enough. And my entry showed that even a terribly handling mess can still podium sometimes, too. Sure, it helps to have a fully prepped race car in GT class, but so what? Aaron's 2015 Mustang is a real daily driven street car and he took 3rd overall with stock power and just good suspension and wheels/tires (18x11 Forgestar CF5s and 315 Falkens). I'm going to drive Aaron's car soon at ECR event and see how much we improved the stock lap times with the new MCS and Vorshlag parts (I managed a 2:06 in it at ECR when it was bone stock).

    I'm glad our Vorshlag entries that had never done this event before trusted me and entered, and they ALL said they had a blast. We even had several in our group that had done this before (Shannon and Jan) and I'm glad they came back with us again.

    In-Car Video BitchFest + New Light on an Old Class

    The video linked below shares 8 minutes of my first hand impressions of the eBay Corvette after driving it at Optima on Saturday. This was the first day I drove this car, and it was a hot mess. I kind of "go off" on the assembly of parts, the aftermarket, some shock brands, and more. The drone and noise from this Borla system was driving me NUTS in traffic, as was the engine's poor idle, terrible driveability, and other glitches (which we've since fixed completely - see below).

    continued below
    Last edited by Fair!; 05-20-2015, 09:07 AM.

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