Petrolburner

I recently bought a nearly all stock C6 Z51 6 speed. It has Z06 wheels, knockoffs I think as it is still running stock size runflats. I'd like to have a car that I can enjoy as a daily driver, road tripper, HPDE, autocross and show car. I'd like to avoid shooting myself in the foot with a modification that will bump me into a class where I have no hope of being competitive. At the end of the day getting on the podium for an autocross that pays zero $ is not the most important thing, but if you're reading this you understand the overwhelming desire to be competitive. I'm also a USFS Pilot so during the fire season I may be unable to make a lot of events.

With the 2014 rule changes, what mods would you suggest to be competitive in A stock? STU? SS? I don't want to buy an extra set of wheels and tires, so if it takes R-comps to be competitive I'm just going to save that for the future. I'd really like to install a healthy sounding exhaust, but even after reading and re-reading the rules, I can't tell what that will do to my classification for autocross. The rules say;

15) Exhaust must exit behind driver or to the side of the car.

3.5 MUFFLERS
Adequate mufflers are required, not so much what it consists of but the overall volume, if too loud the chairman can kick you out.

C. Any part of the exhaust system beyond (downstream from) the headers, may be substitued or removed as long as it exits in the same place

I can't copy and paste from the pdf for some reason so those are approximations. That is from the Street section. So does that mean I can cutout the stock mufflers and replace them with straight pipes and still run A Stock? That is what I have on my Tundra and I love it. The big catalytic converters and the resonator make the small 4.7 V8 sound great under throttle and quiet on the highway.

Here's a picture just for fun



edit: noticed it's not actually called A-stock anymore but A-Street.

Petrolburner

http://www.solomatters.com/street-ca...osal-explained

Reading here was enlightening. I'm thinking I should chop the mufflers out of the exhaust and keep the stock tips and location, and run stock sized 200 treadwear tires like the Bridgestone RE-11.

Petrolburner

No advice on setup? Suitable classes?

RX7 KLR

The C6 is not STU eligible, so that is easy.

If you don't want to buy race rubber Street will be the way to go. I would not worry about power upgrades (exhaust), kind of a losing battle with street rubber - and yes, cat back is open in all classes. Focus on using the power you have, a good set of shocks, and a swaybar package that maximizes corner exit grip.

Petrolburner

I just want to mod the exhaust because I like the sound, way too quiet stock. I want to make sure I don't kick myself up a class for it though. I agree it doesn't need anymore power, especially on street tires. I'll look into shocks and sways.

Ramo7769

Your Z06 knock-offs will be illegal for street category. You need to run stock width wheels. I believe you are allowed to go up or down 1" in diameter.

Acquaint yourself with the rule book. Here is a link to the 2014 draft. Yes, it's a draft, but don't expect many changes to be made this year.

http://scca.cdn.racersites.com/prod/...%20reduced.pdf

Petrolburner

I will have to measure them because they have stock sized tires and they don't look stretched at all. That's part of the reason I think they're knockoffs. Perhaps getting a set of C5 wheels would be the way to go and move down an inch with the new allowances. I can't find anything about tire sizes in the street section of the rules. I assume they need to be stock sized?

Hat_Trick_Hokie

Per his original message, I think they're Z06-style wheels in stock C6 base sizes. So the OP might be okay in that respect.

Good luck with the upcoming auto-x season

Ramo7769

Gotcha, you may be ok then. Definitely measure them so you can be ready to let your competitors measure if they are losing and want to challenge you.

To my knowledge, you can actually run any sized tire you want on stock width wheels within the UTQG tread wear limit. In the old stock category, the only tire rule was DOT legal. The fast guys would run 315 A6s up front on 17x9.5s in SS in a C5 Z06. With street tires, however, I would expect problems putting tires on that are too wide for the wheels. You can get away with it on Hoosiers.

69autoXr

Just be sure to keep in mind that many events have sound restrictions these days. We lost an excellent site in my region several years ago due to noise complaints from the neighbors.

Petrolburner

I measured them with a tape measure last night and got 9" wide in the front and 11" wide in the rear. Of course this was the outside and I think that technically they refer to the inside of the wheel, where the tire mounts, right? I'd have to dismount the tire to measure accurately.

If I can only change one swaybar, which would you change, front or rear? Z51 bars shouldn't be too bad, but the shocks have 74k miles on them and they're almost ten years old. Thinking about ordering the JO package from Pfadt for $1000, but then I'd have to change out a sway bar before and after every autocross, and that's just silly. Perhaps I'd be better off saving the cash and just changing out the shocks. Then if I'm not using the swaybars perhaps the Koni shocks would be better with the Z51 bars.

Ramo7769

It sounds like 8.5" wide fronts and 10.5" wide rears. If that's true, your balance would be thrown off in addition to it being illegal for the class.

I'd just pick up a set of OEM wheels if you want to be legal.

All you're really doing by changing one sway bar is changing front and rear lateral grip relative to one another. I'd recommend getting seat time with the wheel and tire combo you will compete with before changing either sway bar.

69autoXr

The widths may be cast into the back of the spokes (not sure if this is true for aftermarkets but worth a look), pull a wheel off or check with a mirror perhaps. C6 Z51 should be 18x8.5" front and 19x10" rear. From your tape measure numbers, it sounds to me that this is likely what you have. It's not easy to get accurate measurements with a tape measure through the spokes from inside to outside flange.

Petrolburner

Thanks, I'll check the backside of the wheels.

Petrolburner

69autoXr, thanks for the idea. I pulled my wheels off tonight to install the Z06 splash shields and this is what I found;





No longer worried about finding a set of stock wheels, now I just need to burn off the rubber that I bought the car with so I can go stickier.

I also decided today after some more research to snag a set of the discontinued Pfadt adjustable shocks. I know I'd always be wondering, "What if I could go a little softer/stiffer?" if I had non adjustables like the JO shocks from Pfadt. I didn't want to spend the amount necesary to get Koni Yellows if I didn't have to. I found the old Pfadts in a few places, and then found these for $100 less than the others AND free shipping! Placed my order, hoping I don't get a notice tomorrow saying they're out of stock and unavailable.
http://www.trackspecmotorsports.com/...dt-shocks.html

sd7ss

Nice car, Petrolburner!

Fully agree with RX-7 KLR, above. He's been there and done that and has won at Nats.

Go run the car as is at a few events in A Street, and see who your competition is before you invest heavily in mods. Remember you're up against C-6 Grand Sports and Z06s to start with, not to mention a few other quick Auto-X cars in that class. Tires are the most critical element, followed by shocks and then maybe a different front bar.
Also, keep in mind 140 TW tires are allowed this year, but that changes to 200TW for 2015. As you found out, your present wheels should be just fine. Good luck, and have fun!

Best Regards, John

UrbanKnight

C6's are not A stock cars either from my understanding, you are SS, SSP, or SSM

If you go coilovers, thats automatic SSM, everything else you can mod and stay SSP (power mods, sways, etc) SS I beleive you can run stickies (this year based on treadwear), and have a catback, but I think other power mods (Headers, intake etc) put you in SSP.

As you said, unless you are a national champ, autocross is only for your entertainment, but I understand being competitive. I started autocrossing my 2011 GS in August. I have full exhaust, because I enjoy driving the car other than just the autox, so I am SSP... I stopped short of doing coilovers because I didn't want to go to SSM...

Petrolburner

The C7 and C6 ZR1 are in Super Street, the non ZR1 C6s and C5 Z06 are in A-Street. Going up against a similarly prepared LS7 powered C6Z hardly seems fair, but there has to be a limit to the number of classes. I'd rather see the C6Z in SS, but I don't make the rules.

So it seems you can throw any size tire on that you want in the street classes, provided the 140 TW and the rim width is stuck and +/- 1 inch on diameter. Suggestions on what tire would be best for me? Should I plan on getting two seasons out of a set of tires and therefore get a 200 TW tire like the Bridgestone RE-11? Or get something closer to a 140 for this year and run new rubber next year? So far I've only been looking at stock sizes so the RE-11 was about my only choice given the 200TW and size and dollar constraints.

I'm settling up a debt from my friend who wrecked my C5, hence the mods all happening at once.

UrbanKnight

Petrol,
Is that new for 2014? In 2013 the c6's were SS

Petrolburner

That must be new then, the above references are straight out of the 2014 rules. If you read the article I linked in my second post it will explain a bit of their logic which I agree with. I don't want to buy a second set of wheels and R-comps to be competitive in a "stock" class. That's why the name was changed to "Street" class.