goatts

Anyone built a C3 for autox? I know I've seen at least one somewhere on this forum (it had a rollbar). I've had two C3's and I'd like to get another one and autox it. What sort of mods are best? C3 is still one of my favorite body styles. I'm currently using my C6.
Thanks,
Tom

parkerracing

Hi-

Head over to the C3 For Sale section about 1/3rd of the way down BFoster is selling his, ready to go (sorry, but I suck at links). /:\

BLACK SHARK

http://forums.corvetteforum.com/show....php?t=1574776

FB#1

check out 69autoXer.

AUTO_X_AL

He has a very well sorted car.

69autoXr

I built my C3 specifically for autocross, and mostly to the NCCC Group 2 rules. What mods you make depend on who you're going to run with and in what class. Tires obviously make the biggest performance increase, and the lack of available 15" sizes in the most competitive DOT tires pretty much forces the C3's out of stock classes right off the bat. Kumho offers the V710 in a 225/50-15, but other than that you're left with Hoosier DOT bias Street TD's in three 15" sizes, but for the most part these tires will not hang with the 710's or the Hoosier A6's. From there you're forced to upgrade wheel sizes to get competitive tires, then the usual suspension mods (springs, shocks, bars), power upgrades (most legal C3's will be running 70-spec LT-1 motors), and make it as light as possible within the rules.

goatts

69autoXr - you've got a nice looking race car. Did you flare your rear fenders? Do you trailer the car or drive to the races?

Thanks

69autoXr

Fronts and rears are flared-ACI L88 flares. I trailer to events, you never know what can happen with these old cars.

Kalway

ey 69autoxr I'm building my '81 up for SM2 slowly but surely.

First off, what shocks/springs/sway bars are best? I'm gonna definitely go to the vb&p front monoleaf eventually, but what composite rear spring and shocks go together best?

I'll be looking in to some 17" TTII copies from discount tire in the coming months and I think that'll help a TON, obviously.

69autoXr

I can't say what's best, as I haven't tried everything. I can only tell you what has worked for me thus far. I run cut 550 coils in front and a VBP 420 lb/in composite rear spring. 1-1/8" bar in front and factory 7/16" rear bar, though most C2-C3's do not use any rear bar. Shocks are Koni red Classic SA's.

Kalway

Any idea how stiff the 9 leaf FE7 spring in the '81s are? My '81 has the gymkhana suspension, and it's pretty much torture driving on it. It has a 1 1/8" bar up front an like a 3/8" pencil in the back stock.

I'm thinking herb adams approach to the C3 is probably more practical, for a c3, with the lighter springs and stiffer bars. However I think tires will still be the main factor of holding enough lateral gs.

On shocks, I'm still kinda tossed on Konis and Bilsteins. The advantage I'd have with bilsteins are that my mom works right next door to them.

burners

What tire sizes are you running with this setup? I assume that for autoX your setup is slightly on the loose side. Is that the case or is it more neutral?

Kalway

I run a bit of toe out in the front, toe in for the back, and a degree or two of negative camber all the way around. Caster at 2.75 on both sides.

73-84 IMSA Widebody

GoodYear racing Tires are available in 15", I run them.

Kalway

Goodyears are crap, though, and they aren't in 27" diameter. Until I can completely devote my vette to just autocross I have to run street tires. If I were to spend money on race tires I'd probably just use Hoosiers, anyways. $200 a piece and you KNOW they're good.

69autoXr

I currently use 275/45-16 Hoosier A6 radial or Street TD bias on 16x11 all the way around. The car is very neutral with a very slight push at the limit.

69autoXr

No idea on the 9 leaf, but i thought that the springs with fewer leaves were stiffer.

The soft spring/big bar approach may be a better compromise for a car the sees double duty street/track. But the stiff springs maintain the suspension geometry better, which for a C3 is very poorly controlled through the suspension's travel.

73-84 IMSA Widebody

Ouch on the GoodYears They have them in my sizes 25x11-15 r475 and 27x14-15 r430, I'm quite happy with them thru Sasco Sports

69autoXr

It all depends on your application; those Goodyears are a medium hardness compound road race tire, and would probably not work very well for autocross where you need a tire that gets up to temperature quickly. However, for a track day, those tires would be more appropriate than a Hoosier A6 would be. Also, most autocross classes except Prepared and Modified require DOT approved tires.

Kalway

You say you run cut 550 lb. front springs, so your fronts are probably close to what? 600 lb/in? Being that I have the FE7 suspension I've already got 550 lb springs in the front. Now here's a good question.

Would it be worth it to me to go with the dual mount rear spring and the monoleaf front suspension with 1 1/4" and 5/8" sway bars for sort of a dual purpose car? It'll eventually mainly be just for autocross but who knows how long that will be, until I get a good daily driver. My understanding is that the dual mount rear spring has an adjustable spring rate. I'm guessing that coupled with smart struts would give the best rear suspension geometry possible without modifying the hell out of it to fit a 6 link. I know the front monoleaf system is adjustable so that'll easily make it more comfortable to drive around.