TXCatalyst

I come from a long history of tired LT1's in excess of 185k miles and have people that can rebuild strong 4L60E's for cheap.

I've noticed a lot of Vettes in the 100k mile range that are automatics selling for...well, dirt cheap, here and on Ebay.

I've had LT1 cars with high stalls that would knock my head back and shift kits that bark 2nd gear and sometimes 3rd.

I am considering getting an automatic C5 *on-purpose* for autocross and mild time trials. I figure if I rarely shift in an autocross (I personally rarely ever have any need to ever shift my M6 to first) and if I just leave it in 2nd, well, might as well get an automatic that I'll just leave in 2nd (after the 1-2 launch).

I feel bad for putting so many miles on my rare FRC, that I can get an automatic C5 for 50% less!! Sure it will have miles, but I do all my own car work and I won't feel bad, plus once you hit the $10-12k mark, even if I drove it hard for the next 2 years, I wouldn't lose too much on the resale. Certainly less loss than a rare FRC.

Would a stall converter be a bad idea for autocross - I've never kept track of tranny temps. 2400rpm? 2800? 3200?? Too much slipping? If I do that, I'd take the time to do gears too... maybe 4.10s in an A4.

Would appreciate all viewpoints - given the above info.

Solofast

Been there, done that (with a BSP C4), and it can be about as pleasant as having one foot stuck in wet cement....

I guess that it depends on what class you want to run and what rules you are running under. In stock the converter change isn't legal, so that option is gone. In Street Repaired, it is legal and it will help, but the problem is that the four speed auto has such a big space between gears that you end up (with the legal rear end ratios) with an 80+ mph second gear that doesn't have much pull off of slow corners. The six speeds have almost 50% more rear wheel torque due to lower gearing, and that is too much to try to overcome with a converter.

If your class allows it and you do a loose converter, you won't have the ability to steer the car as much with the throttle, since you won't get as much engine braking as with a tight converter.

If you could get a short final drive ratio (like a 4.10) that would really help. Not sure where you are running or if NCCC allows rear end changes in Group II, but that is likely the only way to make it work. The SCCA SP rules limit you to the available ratios, which in a C5 means a 3.42 is the shortest axle ratio that you can use and that results in gearing that is too tall for second to work.

Carolina C4 Racer

FWIW NCCC does allow gear changes in group II as long as the gear is in the stock housing.
AM

TXCatalyst

Thanks, some great points, I don't really race for any particular class or particular rule set - I enjoy having an awesome weekend car and having a blast. The local BMW club puts on 12 events a year or so, the local Porsche Club has 10 autocrosses and 10 time trials a year, and the local S2000 club has 8 autocrosses a year. Amongst all of them a C5 is classified as an Other-American car - no rules, etc. Sure the guy in the Dodge Neon SRT-10 is at a disadvantage, but oh well, I like TTOD in a car I drove there and back, etc. Plus beating the top BMW and top Porsche at their own game is always fun and has kept me busy the last 4 years.

So that being said, no rules, but all out automatic car - is there a recommended stall speed maximum ?? I have no clue what that does to tranny temps in under 90 seconds on an average autocross course. If I chose to go lapping (more rare), I have no idea what happens after 20 minutes a session.

So stall converter, 4.11 gears, cam/heads, 315/335's all allowed - does this paint a better picture for autocrossing an A4 C5 ? (Car will be driven to each event)

Solofast

Maybe others who are running autos can chime in, but the stall speed is really a matter of how you like to drive the car. The trade-off is off of the corner torque versus drivability.

Our BSP car had a converter from a Mvan that was custom modified to give us the stall characteristics that Larry wanted. They were close to stock in torque multiplication, but the converter was smaller and a lot lighter than a corvette unit. In addition, he took the clutch out of the converter to save weight. Neither of those are good ideas if you want to use the car on the street, but it worked for a track only car.

The issue with being that too loose and you will gain off the corners, but there is less engine braking. I like to help turn the car with a subtle lift on turn-in, and tend to work the throttle a bit in saloms and offsets to help turn the car. This is a result of driving stock class C4's for a lot of years that didn't have as much front end bite so I was driving to make the car work. I had to relearn and do away with that when I ran the automatic, because there wasn't enough engine braking to help it turn. So if I was setting it up I'd be going for a tight converter (close to stock) so that I could drive the car like a stick shift car. I know others who have been very successful with a loose converter and a lot of left foot braking, with the car set up for more oversteer, and it worked for them.

XPC5R

We autocross a highly modified C5 with a 4L60E and 4.10 gears. Vigilante 2400 stall with the lockup clutch removed. Manual valve body (transgo shift kit would give you the same thing) The converter actually stalls around 2800rpm behind our H/C motor.

1st gear is very short, but good for jumping off the line, or courses with straight starts. 2nd gear is around 85mph, but there is plenty of punch to burn the tires off all the corners at full stall. The tranny gets hot quick. Keeping it cool is manageable for short autox runs, but it still hits 200-220. Not sure it could be kept cool for a full 20min session.

For autox only, it will work great if you can change the rear gear. I would not reccomend it for track work because of the heat.

Dirty Howie

I track my car...not autocross.

See my sig......A4/402/H&C/3.42/Vig2400 converter.

Works good. Heat is an issue.......get a bigh tranny cooler.

Let me know if you have any questions I can help with.


DH