GIGAPUNK

iTrader: (2)

Im building a 408 L76 powered 240sx and Im trying to decide if I should keep the 4.08s in the rear. I hear that a lot of guys end up running in 3rd gear at the autocross due to traction issues in 2nd, even though that keeps their operating rpm range below most of the powerband. Do you guys struggle for traction in 2nd? Do you autocross in 3rd?

2MCHPWR

iTrader: (10)

25 mph to 70 mph is typical MPH range.
everyone autocross' in 2nd gear except for a few.

mikespeed95

iTrader: (1)

Have you been to an autocross?

The throttle will overwhelm the tires as much as the driver allows it to, it's not an on/off switch. Depending on the class and venue 2-4th gear will be used.

I'd decide a class you'd like to pursue and a venue, asking what gear to run at an autocross is about as vague as asking what gear to run on an oval track between .25 and 1.5 miles in length...

Nuclear Banana

Control the power by rolling into the throttle coming out of the curve. You may be able to use 2nd gear

If that's still hard to do, lug it in 3rd. Autocross times improve by being smooth. If your out there fishtailing and drifting every corner, your loosing time.

GIGAPUNK

iTrader: (2)

I campaigned a 300hp NA miata very successfully in the SCCA, BMWCCA, and PCA. I went through my all of my datalogs once and realized I had never been over 76 mph in a whole season autocrossing the miata. Traction was a pretty iffy concept in the miata, and the new car will have almost twice that power.

With my current tire height, 76 mph wouldnt come until 7200 rpm with the second gear in my t56, which is a little higher than Id care to regularly spin my motor.

If you guys that actually autocross your cars tell me youre regularly in third, than Ill stay with the 4.083s and lug it a bit.

mikespeed95

iTrader: (1)

The problem with asking the whole internet is that some venues are second gear, some are fourth gear, and every course is different.

So you're going to make 600whp, what width and type of tire are you running in what class?

I take it you're just autocrossing for fun, and you're not trying to be class competitive since you'll probably wind up in X-Prepared, any S-chassis with more than 400rwhp is going to be a fight for grip in 3-4 gear, so it's somewhat irrelevant. Just being honest.

GIGAPUNK

iTrader: (2)

...I'm expecting about 485 ftlbs at the flywheel. I've never driven a car with that much power, and with the 275/40/17 falkin 615s I am a little afraid that the throttle will be a bit of an on/off switch.

But if you guys think that my right foot could learn to modulate it, the 3.7 r&p in 1997+ q45s would get me 81 mph in 2nd at 7000 rpm. And I do believe that would work for 95% of autocrosses.

Boss002

Most of the SCCA autocross event i've been two 2nd gear in the camaro is just fine, maybe even a little tall. At 72mph I have just a little tall over the Boss 302 in class that run somewhere in the mid to low 60mph zone. Now the highest MPH I saw was at a larger airport and it was 80mph in 2nd gear on a CP thunderbird.

Now when it comes to "autocross" style events outside of the SCCA who knows what you'll need. I've done one on a race course and hit 4th in an STS miata.

GIGAPUNK

iTrader: (2)

Thanx all! Time to learn finer throttle modulation control. Ive ordered a subframe from a 97 to 01 Infiniti Q45. This will allow me to swap my 4.083 R&P for a 3.69, so that I can stay in 2nd for most courses with top speeds below 84 mph (at 7250 rpm). It will also allow me to use the Q45s beefier axles and hub bearings, though I'll have to shorten one of the axles, and use the 5 bolt, stub axles from a NA z32 300zx so that I can use my 29 spline r200 obx torsen lsd.