Best LSD for the job?

[E turd]

I currently have a stock 325i w/ manual tranny that I'd like to put an LSD onto. After some reading, I've gathered that I should get a medium case and that a lower ratio means longer gears and better gas mileage. I don't really care about either of those much. The car sees weekend solo autocross action 1-2 times a month so installing LSD will be done primarily for that.


I'm guessing either the 3.73 or 4.10? Any suggestions from experience or superior knowledge? Is there a better ratio? Car to pick the LSD out of? Fluid of choice?



Thanks!

[jlevie]

For autox use, a 4.10 would be better than a 3.73. And for a limited slip differential, I prefer Redline 75w90.

[Teaguer]

For autox use, a 4.10 would be better than a 3.73. And for a limited slip differential, I prefer Redline 75w90.

Well on paper it would seem so ....but is not necessarily the case.
It really depends on the type of course, sure the 4.10 would new better acceleration but if you have to shift to 3rd several times because of the course then it could be slower.

Ideally the all around best ratio would be the 3.73 ....hell thats why ALL manual US e30 325i's came with them as stock.

But having said that ...... I have auto-x'd several e30's with a 3.73 and the 4.10 and also currently daily a 4.10.
Yes by far the most fun to be had is with the 4.10.

To source the 3.73 just look for any manual 325is as they had the LSD as stock.
While the 89+ 325is automatics had the 4.10LSD as stock.
Also the US e30 M3 had the 4.10LSD.

[RangerGress]

Buy my 4.10LSD. I pulled it off of my parts car and tested the clutches at 50ftlbs so it's cherry. $350 shipped.

[Farbin Kaiber]

25

[E turd]

Thanks for the help guys. I'll try to find the 4.10 out of the late model is automatic as suggested. On a side note, I read about using the M coupe bushing as an upgrade. Any one have the part number for that off hand? I tried to search and only came up with the number for the finned cover with the bushing already installed.

[ThreeTwentyFissel]

Whats the benifit of the 3.73 over the 4.10, daily driving in mind?

[jlevie]

The 3.73 results in lower engine speed for a given gear and road speed thus yielding better fuel economy and a higher top speed at the expense of acceleration.