Auto Crossed my Z51, 6sp 1990 C4 today. 1st time. Suspension links, joints, etc are new or in very good shape, shocks are recent Koni adjustables. Started with air pressure at 36 all around, went up as the tires got hot. Started backing down in increments of 2 then 3. At 30lbs front and rear the car was much more controlable, however it was easy to rotate the rear of the car with the throttle. Spun more than once.

Question is it just lack of experienc and skill on my part, or should I look for a part problem (after all I am the greatest driver in So Cal. [not])

Best way to correct.

 

I just got my first Vette and I found the same thing, there is no hanging the tail out for me. There is an easy adjust caber setting in the rear that might help you a bit at the autocross and set it back for the street. It's marked so just find your marks and adjust it.
But yes, the drift angle seems to be very very small IMO, I can take a v8 s10 and hang the tail out, this vette I have tried and the tail wants to come around fast so I will not be trying to slide around any corners personally (which is a favorite of mine). It's a point and shoot car I think.. is what this means is drive a little deep into the corner and take a late apex (search google for late apex).
http://www.drivingfast.net/techniques/racing-line.htm

also, on many performance rear tires there are little triangles, when you come off the track the road wear should just touch the tip of these triangles, that is when you have the tire pressure set correctly. Next take a laser heat gun and check the tire temp across the tires tread, too much camber the inside of the tire will be hot, not enough camber the outside will be hot and just the right amount the tire will be even across it's tread.

so mark your street camber setting with a punch or chisel (or use a permanent marker) and get to adjusting for the best contact patch, once found mark that spot also. now you can easily adjust for street or track (both settings will provide an even tread temp for their purpose, more side load, more camber).

another thing you can do is to soften the front sway bar but this will hurt feel and corner entry speed, if you have body roll a stiffer rear sway bar will help keep the inner tire planted

 

You want the car to rotate on corner entry. Then when you get on the throttle on exit, the rear will stick without terminal understeer. Ideal autocrosser will be looser than ideal road racer.

Book says your car has a 24 mm rear bar, and the '91 went to a 26 with everything else the same. So Chevy thought your car needed more oversteer...?

I spun my '92 Z07 many times in my first year, and never did after that. My favorite spin was a full 360 without touching a cone. I got applause for that one!

I'd keep it stock for now and play with tire pressures.

Have fun!

Bill

 

Suggest getting some track tires. Tires continue to cure & get harder with each heat cycle. If your street tires have 10K or more on them they will probably durometer out high 70's - low 80's which = a poor handling track vehicle. A durometer tests rubber hardness.
Suggest tires that durometer about 55. They will be soft enough to provide good adhesion & last for a number of track days. A tire that is to soft will shed rubber like a pencil eraser on a hot day & cause a "loose" handling vehicle. However, for auto x without warm up laps a soft tire that durometers in the mid to high 40's may be a better option for you.

Seat time: You can never get enough. Fast corners are an aquired skill. Suggest smooth transitions & applications of/from throttle to brake & back to throttle. Spinning the tires on corner exit = slower lap times.

If you have the FX3 option try some laps in the tour or sport setting to see if the laps are faster. Stiff suspension = less tire compliance & slower laps.

Good luck.

 

'nastycar' owners throw a foolhardy teenager into the driver seat and set the car to understeer (aka 'push', aka 'tite') to reduce equipment destruction...if you're 'looping it' too often, you might try running front tires 2-6 lb more than rears, or disconnecting rear roll bar, to produce understeer when not under power...rapid or excessive throttle in a rear wheel drive car with 'adequate' engine output may still 'let it all hang out'

 

Check the alignment of your rear toe in. For fast auto crossing you would be better having about 1/8th inch toe-in to control the oversteer issues. Good Luck. MSTRS 2

 

Check your alignment

here's a good starting page
http://www.vbandp.com/instructions/h...ruct/align.htm

 

I agree with others on checking the alignment. For autocrossing the rear should have around -1 to -1.5 chamber and about 1/8 to 3/16 TOTAL toe IN.

 

Best advice!

 

Not sure on the 90, but the 94 tire pressure is 30psi cold. Adjusting at the track would not give you the correct cold setting. I also recomend starting with tire pressure first.

 

If this was your first event, then the best possible thing you can do is to get seat time. Enter more events, ask experienced drivers if you could walk the course with them and ask a few questions about where you are having problems in a particular type of turn or corner.

At this point, you would not really be able to tell the difference in how a change in alignment settings will affect the car. And going too far with a specific alignment setting can cause handling problems on the street.

If you are losing control and spinning, my take is that you are applying too much power too soon. Try braking before turn initiation and keep a steady speed thru the apex. As you exit the turn you can begin to apply power once the car is straight. Lots of autocrossers will tell you that you have to go slow to go fast. Car control in a turn is more important than how fast you can go especially for a novice driver.

You can play with tire pressures but unless you watch how you apply power, you can still break the rear end loose even at 25 psi in the rear. You didn't say what brand/model tires you have but not all tires react the same way to the same pressure.

I went 3 years before I even considered running slicks. There are too many things you can do to a car in terms of tuning the suspension and using driving techniques before jumping into race tires. You have to figure out what the car is doing after each major change.

And the number one thing is seat time. Enter lots of events. That gets you a chance to understand the car, learn to walk the course and figure out how you will drive it. Course always change; longer, shorter, more turns, less turns, technical areas, easy areas and such.

Oh, get more seat time!!

 

I was under 30psi when I was at autocross.

But how old are your tires? The ones that were on my car when I bought it had plenty of tread depth but were old and the rubber wasn't what it used to be. There was no real transition from sliding to spinning. Putting a new set of tires on mine made a night and day difference.

 

Newer tires help, but also try at least a 2 psi spread front to rear (more up front). This helps a lot too. I start cold with 28 front and 26 rear and keep them at 36 front 34 rear hot.

 

Practice throttle control on exit by "autocrossing in the rain"!
My guess is your getting on the throttle too hard, too fast on exit.

I agree with earlier posts on rear "toe-in", if the rear is not toe-ed in a bit, the rear will be all over the place when "on throttle" exiting a corner.

 

I have an 89 Z51 and have autocrossed it for about two years. I had the same problem. Spun the car several times. Throttle oversteer is pretty easily corrected with practice and throttle conrol but the trailbraking oversteer was causing the biggest problem. I corrected it by putting a larger front sway bar on the front with poly bushings. Completely settled it down. I can now run very hard into corners with no worries of breaking loose. Car is still very nuetral and didn't cause any understeer.

 

Auto cross is a disease. I caught it sevral years ago and went every month for 2 years. Three things jumped out at me as I progressed, SEAT TIME IS THE MOST IMPORTANT, next I went with 11" wheels on the rear, and then went to school on how to keep all four wheels biting in the turns. What worked for me was to think of the turn as 3 separate parts, preturn, turn, exit. Preturn- approaching the turn at speed you need to find the point where hard braking (no skidding) will allow you to enter the turn without braking. This puts the center of gravity more towards the center allowing more centralized weight on all the wheels. So, you need to know what max speed will allow you to make the turn. This takes practice, trial and error. Keep a record of speed entries on each turn. Think of a bottle of water in your hand sideways. Braking the water will go forward leaving the rear light. Same with your Vette, braking is not the time to turn as your rear wheels will lighten and step out. On a previous reply here, he mentioned driving on wet pavement, good idea and time to practice a preturn. The question is where to practice. THE TURN, As I start the turn, I release the brakes and have the throttle ready to go (some guys use the "tow heel" ). Half way through the turn, I start adding throttle so that I'm all out by the end of the turn. Remember the weight is now more towards the rear as you want max traction there. If she starts skidding, ease off and note where you added the gas. I hope you get the idea. It's not the only technique, just one that worked for me.