3.23 Lsd
 

I've had a suggestion to get a 3.23 LSD diff for my car... but right now mine stock has a 3.91, so wouldn't I LOSE torque in that conversion, or is there something I'm not understanding about diffs?

You don't have a 3.91, you have a 2.91. And yours is an open diff as opposed to the limited slip diff. Trust me, if you want quicker acceleration you want a 3.23 from an m3.

hope it helps

Gotcha. Can someone explain the difference in limited slip and an open diff? I've always wondered that but never known. :)

Limited slip, (in the case of my car uses disk like a clutch) prevents a traction-less wheel from uselessly spinning, open diff allows this wheel spin, frustrating in slippery situations, but slightly more efficient in terms of friction ;)

i upgraded to a 3.23 lsd from an open 2.93 and it made a huge difference in traction and acceleration. a very worth while upgrade for a manual, but not to sure about it for an auto.

not worth it in an auto.. stick with what you got...

In lamest terms, open diff = one wheel burnout; LSD = both.

I think you should go for a 3.23. Yeah, it will probably be loud and as un-economical as shit on the highway, but who cares.

US Auto cars have it perfect 3.91 is has good as it gets for Auto E36's

If you feel your car doesn't "accelerate" quic enough, drive a truck or a normal car for a day, and when you get behind the wheels of your car, you'll see what I mean.

So an LSD is the same as a posi?

How would a 3.91 open vs a 3.23 LSD differ if the car is an auto or manual? How would that change things?

yes possi is the same thing as LSD...

it changes your geating ratio'...s with a 23 you're top end will be higher in speed but and you might gain a little more grip from the beginning... I would take that money and use it for going 5spd personally.. an auto with a LSD is pretty much useless imo.

Yes but if you have enough power to make the inner wheels spin and loose traction during a turn, then an LSD would be benificial now wouldn't it?
Open diffs suck, they are no fun at all.

yes, LSD==positraction. I prefer to say LSD since positraction is a ford\chevy term.

Read this: http://auto.howstuffworks.com/differential.htm
Viscus LSD's are awful for preformance (as you can see, there is no SOLID connection, same thing that makes automatic transmissions suck [the torque converter]). Quaife sucks for racing since once one wheel reaches zero traction, the torque bias suddenly becomse 100% to that wheel, basically an overly complex open diff. Clutchpacks are great for racing & preformance and there is no loss of power from the clutches. Nascar uses a detroit locker diff that locks the rear axles together completely under load, Great for foreward traction, but suck for turns, not really important to them is it? :P

If you have a 3.91 now, going to a 3.23 would be worse. I have only looked into this for 5 speed manuals. Im guessing you have a 4 speed auto, so your tranny gearing ratio is way different than a 5 speed manual. Im thinking that this would reek havoc on your auto tranny if you played around with the gearing ratios.

It wouldn't cause havoc, it would just shift differently. It calculates when to shift based on RPM, current speed, and gas pedal positions. If it does suck somehow, you can always go into steptronic mode. The automatics don't downshift until the RPMs are somewhere below 1,000 so they wont accidentally over-rev unless you go into steptronic and it's lower gear RPM prediction is too low due to the ratiochange, so I guess just be careful when doing that.

I heard from someone at a BMW dealership that they reset my "computer" and my transmission will "re-learn my driving style" when it was in for some reapairs, so it may very well automatically detect each gear's sped limits based on whatever gearing ratio it's hooked up to.