Best gear diffs and why???
 

What are the best gear diff's to run for my 1995 M3. I heard you can really imporve your track/daily driving from doing this. I plan to do some auto X and track driving. I heard 3.46 was the best, why? and what will this do to overall gearing? more narrow or wider?

Not sure what is the absolute best. I have a used 3:45 from an auto and man that thing has some low end power quick and fast when I put it in haha.

it all depends on what you want... you said you want to get into some autox.... but how fast do you drive say on the freeway, do you race anyone? you want to make sure you dont get geared to high. In that case you would fly to your top speed, but as you probably know the top speed wouldnt be that high.... personally i really like the 3.46

if you want a comparision of rpms to mph with different diffs go to http://www.diffsonline.com/

and click rpm/mph and pick with diff you are looking at

Hope this helps you out

David

what is the ratio of the differential that can go 3rd gear 110? b/c the others can like go 3rd gear 85

maybe a 2.79? it says at at 7000rpm in 3rd you will be doing 112 mph 185mph in 5th and 7000...

David

I think the best overall diff for the average user/tracker is going to be the 3:15LSD which is what I use. I think this comes stock on m3s though doesn't it?

wow, i was just about to start a thread like this. Good for people to know that they don't need to throw thousands at their engine to get the speeds and acceleration they are looking for.

It sounds to me like a 3.15LSD is a very well rounded diff.

OK, beffore you do a gear change, take this into consideration.
When changing gears, your engine will rev alot faster theirfore, giving you more low end torque. HOWEVER, even thought you will gain low end torque, you will loose some high end torque and you will reduce your engine's life, I really asked around the pros a lot on gear ratio changes bcs I changed mine on my mustang + since I changed my ratio, I had to get my speedometer re-adjusted

3.15 95 m3
3.23 96-99 m3 manaul and 95 m3 auto
3.38 96-99 m3 auto

i went with a 3.23 because it is a big improvement over the 2.93 open diff and is very manegable for a daily driver. a 3.38 is supposed to be the best oem diff because it gives great acceleration and still has a decent top end. i would have bought a 3.38 but they are much more rare and command a premium price. when installing a new diff you will not need to have your speedo adjusted because there is a sensor in the diff that tells the car the proper speeds with the new gearing.

how would having closer ratio gears reduce the engines life?

Yes, Bmw have that and I love it, if only mu mustang had that it would have saved me $92.... :mad

bcs your engine will rev up faster theirfor will rev more higher rpms = more force implied on engine = lower life for engine

just becaus the engine revs up faster, that doesnt necessarily mean that it will rev to higher RPMs.

the only way it will rev to higher RPMs is if you actually push the throttle and wait for it, i can have the crappiest ford escort with the weakest engine, and still rev it up to 7000 if i wanted to

I think he means that since the engine's RPM's will generally be a good deal higher than they use to be, especially during crusing speeds, it will wear out faster.

The engine wind up faster, I don't think that's the issue, the issue is that because the engine is generally in the higher RPM's more after you do this. We all know there's a rev limiter, I'm sure we've all felt it one time or another... ESP. you three pedal club members.

If you keep them down by shifting sooner than you do in normal daily driving, then nothing bad will happen.

engines die anyways... have fun with them while you can.. its all part of modding your car

David

(sorry thats my outlook)

Yah, Word.
These engines are designed to make shit rotate, why not make it do it's job even easier by making the ring gear taller?