Ideal 2nd gear speed for Autocross?

[wheelman]

I just acquired a 3.90 ratio R200 for a great price (free) and am debating whether to run it vs. the 3.54 for autocross.

I figured out that with the 3.54 I hit the rev limiter in 2nd gear at ~64.7mph, with the 3.90 I'd hit it at ~58.8mph. I could raise the rev limiter a little from 6000rpm to 6300rpm and gain a few mph but not sure it's worth the extra wear on the engine.

 

So the question is, what is the ideal speed to hit the rev limiter in 2nd considering the car is basically dedicated to autocross?

[Drax240z]

I find the 3.54 works well at my local events - mostly slow speed slaloms. I rarely if ever shift out of 2nd gear, and with more torque on tap as V8/Turbo swaps tend to have, the car pulls from 2500rpm in slow speed corner exits and right to redline.

[JMortensen]

It depends on how tight your local courses are. The less shifting to third you need to do the better. If you have the power you might consider starting in 2nd too.

[SHADY280]

i have 3.9's in my car with a l-series. but my local courses are tight. although i hit 7000rpm sometimes on a bigger course. never use 3rd either. at 64 mph, id still be in second, i also have a 82 transmission. maybe with a early 5 speed it may be different

[wheelman]

It sounds like I should just stick with the 3.54.

Our local courses aren't overly tight but the surface is low grip which tends to keep the speeds down. I can only remember hitting the limiter in 2nd a couple times and shifting to third once.

[johnc]

70 mph in second is good. Per the data collection I've seen, a perfect shift costs .3 seconds on an autocross course.

[Drax240z]

70 mph in second is good. Per the data collection I've seen, a perfect shift costs .3 seconds on an autocross course.

 

Wow, that's a lot of time!

[johnc]

That's what I said and didn't believe it until I saw the data from a couple different cars and drivers. The data acquisition guy did an overlay of the same driver upshifting and not and at the end of a 65 second course the difference was that one upshft.

 

Its not just the shift, its the time between lifting off the throttle and being back on the throttle. The downshift doesn't usually matter if you're good at heel/toe because ideally you're braking while downshifting from 3rd to second.

[RTz]

John, To clarify, you're saying the shift added .3 to the total time, not just .3 to complete the shift, correct?

[johnc]

Yes. The shift took .65 seconds (measured from acceleration peak to acceleration peak) which translated to .3 seconds at the end of the run. The faster run had the car on the rev limiter for about 3.5 seconds.

[JMortensen]

Yes. The shift took .65 seconds (measured from acceleration peak to acceleration peak) which translated to .3 seconds at the end of the run. The faster run had the car on the rev limiter for about 3.5 seconds.

It's not just upshifting that loses speed. I learned that one a long time ago when I let a guy with a little slower than mine drive my car. He beat me by about 1/2 second in my own car. There was a slalom to an end cone which had to be turned around and then you slalomed back. He kept it in second and bogged around the cone. I downshifted to first and then back to second. His way was faster.