What's your final gear ratio?

[PiercedE30]

Ok. I did the inaugural run of the 330 yesterday at an autox. The 4.10 was AWESOME on the course that we had. I wish I had been able to get video, but my batteries, all three pairs, were crap. I was able to stay in 2nd gear the whole time. I was running in SM and was a mere one second off the fastest SM car (Mustang). I placed 4th out of about 10 SM entries. Awesome gearing for autox'ing.

[Stu]

3.73 with a 3.0L M50 and Getrag 260.

I like this gear for the highway, though around town there are times when I'd rather have a 3.46 or maybe even 3.25. 3.73 works well on the highway for me, I drive about 68-70mph and get killer gas mileage with this diff.

On my local track (CMP), the 3.73 works well but a 3.91/4.10 would be better. I've run the track with stock sized tires and with super short tires (equated roughly 3.95 gearing, and I could negotiate the back section much better in 3rd gear by not dropping below 4000rpm. Through the higher speed corners, I was able to use 4th instead of being at the top of 3rd...I prefer not to be at 6000+ through a steady state sweeper.

All in all...the 3.73 is a great gear for an M20 'i' car, an M50/E30 or even a 318is.

[evil_twin]

4.10 welded in a '89 3.25i. I'm using my car to drift though.

[Hick]

3.73LS in a '91 318is

[delatlanta1281]

4.10
not that it matters. I haven't touched a track with this car.

[rsafier]

On a M20 AutoX car depends on the course. If your running smaller local events with tight and fairly compact lots then a 4.10 probably will work better as you won't need to worry about running out of 2nd gear often. Larger courses and anything at more then local level generally are much more open (faster) so a 3.73 works better, or a legal swap of a 3.64 (I think from the iX but you change to the clutch pack LSD) might be better option.

As for FI cars if you have street tires 2.93 seems the way to go you need to limit torque. I found with enough grip tho it can be hard not to bog. on my 285 r-comps I'm running a 3.25, works pretty good tho still can bog. a 3.46 might be a good option but could make 1st even more useless and 2nd harder too hook up when your in the 300+rwhp range. The advantage would be quicker back into the boost off slow corners. Plus depending on the track you might run out of 2nd. I find most of the time I just kiss the rev limit (I use 6500rpm) on most courses that are larger. Only have been to one site that was setup in a way that required 3rd gear.
Main factors are your power level, and the courses you run, pick a gear that will keep you in a good power range coming off of corners.

[Mulholland]

By the math.. with a 2.92

1st. 34
2nd. 60
3rd. 94
4th. 131
5th. 162

^^^stock eta with a 5400rpm redline... I am looking for a 3.25LSD locally, which should make the car considerably faster up top I think. I pretty much top out drag limited in 4th right before redline, only grabbing 5th on a top speed run for an extra bit of umph to top out. The chip makes a world of a difference, but it also makes the 2.93 feel even more docile.

[e30polak]

I went from a 4.10 to a 3.25 in my car and it's a catch 22. I miss the torque in 2nd-4th, but 1st gear was useless. With the e36 tranny and the 4.10 I redlined 1st at like 22 mph at 7300K. Anyway the 3.25 is nice round town, 3rd and 4th are super long, but i want more torque down low before vanos really hits. I'm either goin to switch to 3.46 or 3.73 to get more torque back without having to shorten the gears too much.

[gearheadE30]

I need the 4.10, but I have an M42. For you (and all of the other M20's I've driven) the 4.10 is too short. That motor just doesn't like to rev as much as the M42, and it isn't as happy or efficient doing so. I'd go 3.73 or 3.91 if you can find one.

[nando]

4.10s with a 7k redline - on some of the power courses I'm on the redline a lot, but for many of the more technical ones it's perfect. I would like to raise the redline another 200rpm or so, and I know the engine could take it, but my cam is way past it's peak range by that point. I data logged my last autox, and beating the shit out of the redline I hit 7150rpm along the way - worked out to be around 58mph.

[Gleb]

Just ordered a ZF S5-31 tranny, new driveshaft, 3:46 4-disk diff and an M5 clutch+LTW flywheel from Metric Mechanic:D
Turning my E30 into a race car, will let you know how it goes with the diff.

[E30_fiend]

3.73 seems to be the right diff for a lot of applications. Its like the perfect ratio. Not too tall not to short and its still lsd.


E30Fiend

[bam2002]

I would say on an engine that can rev to 6 or 7 K a 4:10 would be OK for an Autocross. But it be way to high for a track day.
A 3:25 to 3:75 would be better for a track, So if your looking for an All in one Diff.. then the 3:7x would be best.

[rwh11385]

3.73. I had a 4.10. Top of 2nd is more useful for autocross. I can carry more speed in 3rd at the track with the 3.73. Of course, most of the turns I now carry in 4th even with the 3.73...

but don't upgrade your diff unless you swap i'd say. not a huge difference. not that i won't reinstall my 4.10 after the bearing is replaced, but it's not worth the $$ I paid...

[PiercedE30]

I've got a 4.10 LSD, like DSP. Cruising at 80 my RPM's are at about 3700-3800. My rev limiter is set for 7200. I also don't have to worry about breaking rocker arms though.