theamxguy

Hello guys. I am headed to Road Atlanta on April 13 with Atlanta Driving Society. I have driven a lemons C4 Corvette there in competition in 2019. The car would run 1:53 with our fastest team drivers. I am taking my C5 coupe on stock springs and shocks and 35/25 Progress sway bars. The car also has an oversize radiator and generally stays at 220 or so on track even in 90+ degree summer heat. I took it to RA last summer and was on small 275.35/18 square Federal RS/RR tires on 18 inch C5 Z06 replicas. ABS module was not working, had the rear bar on middle setting and had equal pads front and rear (Powerstop track ready) Also running Prospeed RS 683 brake fluid. . Obviously the car was a tail wagger! Ran 1;47;3 in 93 degree heat. Turns out the car had a terrible front end alignment and was as low as it could go on stock bolts. Nothing to write home bragging about. The car does have a BTR stage 4 cam (Not optimum for road course work) and Texas Speed long tubes and 3 inch x pipe and LG big 3 exhaust
So in preparation for the upcoming track day, I adjusted ride height to 4.25 at the front jack point and 4.5 at the rear jack point. I attempted to get a proper alignment. The driver's side looked decent with -2.8 camber, 0 toe and 6.9 caster. The passenger side of the car would only go -1.8 camber, 0 toe and 4.5 caster. I knew the car had been hit, but it was on a frame machine and supposedly fixed. Anyway , we matched the left and right sides on camber and caster (-1.8, and 4.5) Not optimum, but way better than it was when it rolled into the shop (less than -.7 camber on one side and -.4 on other side with caster being 6.9 on one side and 3.9 on the other!) Went -1 camber and 1/16th toe in on the rear. I then put Pirelli scrubs on the car 305/645/18 front on 18x10.5 Z06 replicas and 325/660/18 on 18x12 Z06 replicas. Rear has a little poke, but not too bad. Narrower than the 335 series BFG's that were on the car when I bought it. I know the car is seriously camber challenged to be on slicks and is very sub optimal at these settings. Driven on some twisty East Tennessee back roads the car feels much more planted than before. I understand the Pirellis are like ice for the first couple of laps, so I will take it easy on track at first.
Put Cobalt XR1 pads on front of car and fresh Powerstop track pads on the rear. ABS fixer fixed my ABS module for me and it works well now. Moved the rear swaybar to the softest setting. I am adding Improved Racing pan baffles and run Redline 10w40 oil 1 quart over full. I have redline D4 in the transmission and 75/90 in the rearend as well. Also have water wetter in the radiator.
With the slicks /swaybars/ and soft stock springs do you think the car will pull enough G-force to cause oiling problems with the IR pan baffles and batwing pan?
The car has no aero on it and runs 141 mph by turn 9. With the previous terrible combination, I would lift throttle at 9 and coast down the hill and brake at the motul sign. Over 135 or so the rear of the car started feeling a little light and the brakes weren't optimum so I was somewhat cautious. I know my brakes still aren't perfectly matched, but I am using up my collection of stock size brake pads before moving to the big brake kit (likely Wilwood 14 inch competition kit with thermlock pistons and floating calipers), Hopefully the softer rear brakes and softer rear bar will allow me to trail brake, something the last combo didn't tolerate. I believe the car needs monoballs, a better alignment (frame pulled or Borg offset Delrin bushings?) and a proper coilover setup ( I will likely try the G-Speed nonadjustable Bilstein based kit to start with). I will also do AMT camber plates. The car does have a race seat in it already, ( Bimarco Futura).. I hope to add Track Spec hood vents and maybe a NLR wing and splitter.
Am I missing anything obvious to you more veteran drivers? What would you change in order to optimize the car for Road Atlanta? I also daily drive the car and my tolerance for squeaks, rattles and harshness is very high so don't hold back on recommendations.. Thanks in advance for your counsel!

theamxguy

I forgot to mention the height measurements before I adjusted it was 3.75 inch at front jack point and 3.5 inch at the rear. Way too low and a reverse rake.

theamxguy

Also noted that the "floating calipers" I mentioned above were a figment of my late night imagination. I meant to say floating rotors! (AMT C6 Z06, or Girodisc).

jstout

What you need at this point is seat time. I would even had suggested staying on street tires until you really feel like you are maxxing out the car. Street tires give you way more warning than slicks. I have no experience with Pirelli's but you will need to manage your tire pressures. It wont be hot, but you will be pushing the car harder than ever before. Maybe someone can tell you what the optimum tire pressure is once warmed up, and you can adjust the rest of the day to try to not exceed that pressure. Above optimal and tires will get greasy I have a little experience at RA and managed a 1:28.5 in time trials in a C6 Z06.

RX82Z06

A well aligned & balanced stock C5Z is a fast car. I would have gone with good 200TW tires, AMT camber plates to get a better camber set-up, & more rake (3/4”). The big Progress bars should be fine. Assuming you get up to proper temps/pressures on the slicks, at those grip levels you’ll likely find the car takes much more time to take a ‘set’ as all those rubber bushings, leafs, and relatively soft shocks will combine for a lot of travel. The LS6 with batwing pan is proven stout/reliable as long as you have plenty of oil in there. Let’s connect next week, I’ll be there instructing and happy to share some other thoughts on reliability and handling.

TomF

theamxguy

Thanks a bunch for the replies. I agree seat time is the best teacher. I will watch pressures in the Pirelli's. From what I have read they like 31 to 33 psi hot, with a couple psi less in the rear. I have run on Hoosier R6 tires and Hoosier slicks before, but it has been a few years, so I have some distant familiarity with the lack of feedback from a competition tire. This will be the first time on Pirelli scrubs. JStout, a 128.5 is flying at RA! I may change the rake based on your recommendations TomF. I will run it one quart over full and hopefully it will be fine. I will look for you at the event and hope to pick your brain for more ideas. Thank you both for the replies.

davidfarmer

my ST3 car has runs 1:29/1:30...275 tires and only 280hp. We do run some aero however. The big thing at Road Atlanta is to avoid the temptation to turn and apex early. The Concrete tends to suck people into cheating into the corners, which only slows your apex and tightens your exit.

I made this video for a friend last year, he was turning in early everywhere. Every lap is unique, but I find clients do better in the long run when I am rigid with their line early as they learn a new track.

theamxguy

Thank you David! 280 hp and 275 size tires and 1;29/130 is mind boggling! Are those 275 tires Hoosier A7's? Thank you for the video, I will try to learn from it!

jstout

My best to you. Hope you had a great experience. Jerry

theamxguy

Thanks for the pointers guys. The car ran well and had only one issue. The alignment shop had forgotten to tighten the bolts on the driver's side control arm and I experienced some lack of turning ability at 138 mph at turn 9. Thank God it did not cause an accident and was easily remedied in the pits since I had asked them to paint mark the alignment settings. The brake bias was excellent and the pirellis gripped up pretty well after 1.5 laps or so. The car went 144.4 which is a 2.9 second improvement over last track day. Nice to meet you and Leroy at the track TomF.. My new nickname for the car is now SPONGE BOB STICKY FEET! The soft springs and bushings have got to go! I absolutely loved the balance the car had with the big progress bars 35/25 with the rear on the softest setting. I think the 305/645/18 and 325/660/18 Pirellis helped the balance as well. The car was neutral at the limit. Hope to get out again soon. If anyone has an old set of T-1 springs or used good quality coilovers let me know.

theamxguy

I will never go to the track again without checking all the bolts the alignment shop touched.

theamxguy

Sadly, even after watching your great video David Farmer, I was still fighting the early turn in bug. But I did much better than I would have without the video. Thanks again for sharing it.