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Unread 06-29-2015, 11:02 AM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default 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: 93F 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 at 03:55 PM.
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