3.91 LSD? comments/recommendations?

[rwh11385]

I know SimonUK has one, as they came standard on 325i Sport.

When I get my rear subframe bushings replaced, I'll be dropping down the diff anyway, so switching it would be a good use of time. I'm hoping to stick with my promise to myself to keep my B25 stock, so a shorter gearing would help with performance.

Has anyone driven a 3.91, as compared to 3.73LS or 4.10LS?
I don't think 4.10 is the way for me, as I will be commuting an hour away from home to college every weekend, or every other.

I do want some more performance, but is the 3.91 worth it? Fun? I'm thinking it would be a good compromise.

Is it easy to pick up in the states? ~ How much?

Thanks guys.

[MR 325]

I can't answer your questions... [Yes, this post is useless]

But what SHOULD be interesting is me taking out my 2.79 and putting in a 3.73!

[rs4pro3]

I've got a 3.91 lsd in my 85 318i and then my 88 325is has the 3.73 lsd I can tell a difference as the 318i accelerates faster up untill the point the 325i comes onto the cam, the 3.91 has got a lot of low down speed. as I can get the underpowered 318i up to 40 in a short parking lot no problems.

[decay]

my experience totals to having the stock 3.73LS in and swapping it out with a 3.91LS-

i've never regretted it for a moment.

in-town gas mileage is slightly decreased, and of course you shift more, but it's about the same on the freeway; i generally cruise @ 3500rpm.

so yeah, i recommend it.

[Bryson]

god damn, the 3.73ls is too short to begin with...

[Paul Q]

I changed from a 3:73 to a 4:10 and I didn't see any negative to driving a freeway speeds.

I know it could cause poor gas mileage and it should increase the cruising RPM but in both cases it's not that bad. I don't see any problems with gas mileage and the RPM difference at cruising speed isn't noticable.

Paul Q
89 325ic

[Bryson]

you guys are much more tolerant than I, when I had my 4.10:1 highway driving was a pain and all the gears were too short, the car hit rev limiter in 5th way too fast for how waffleswaffleswaffleswaffleswaffles the engine was

[M-technik-3]

Ok my US car had 3.73 and sucked ass. Slushbox. But my Euro one had 3.91 and it was good but I went to 4.10 and it was great. The loss of 8 mph who cares. The fun factor of breaking rear loose when ever I wanted was fun.

3.91 are a great compromise, when I get my sealand van here shortly I will be putting in all sorts of stuff. Prepare for the invasion, Greg style.

[rwh11385]

Bryson,
You hit the rev limiter in 5th? Dang, crazy......on what road?

Greg,
thanks for the input. :up: You bringing a 3.91LS over?

I like the power of the M20, and the 3.73, but when I went from the oversized tires (and taller gear ratio), the right sized tires and shorter gear ratio was a blast.

However, I don't think I'm extreme enough for a 4.10. Most of my miles are in the city, stoplight to stoplight, but I do get out of the highway, and don't think cruising at 4000+ plus would be fun. Just yeah, a compromise would be good.

I'm not sure when I'm going to be pulling all this stuff. There's no real rush, and it might have to wait until next summer, or maybe just winter break. Got other things to do, like starting college, and don't really have the $ to throw down. (Otherwise, I'd be jumping on Kansas-IX's 3.91) But when the subframe comes down, it'd be cool to have a 3.91LS to put in there.

thanks guys. Any other opinions??? Simon?

[AdamF 88iS]

My coworkers car has a 3.91ls in it. It's a good compromise; I feel that an M20 without a chip runs out of rpms kinda quick with a 4.10.

And BTW, don't panic about finding one. 1989 635CSi.....thats all i have to say.

[Bryson]

I feel that an M20 without a chip runs out of rpms kinda quick with a 4.10

agreed, but even with a chip it's too short

Robert - I hit rev limiter in 5th with a bone stock m20 and the 4.10 (137mph on many roads) and rev limiter in 5th with the m30 AFM and those injectors I traded you with the 3.73 (151mph on I-52)

[rwh11385]

I don't need to be going past 120+ mph, so I'm cool with a little less tach.

1989 635CSi? Tight, thanks Adam. :up:

I was driving tonight, and looking at my tach and 4.10 5th is pretty much a 3.73 4th gear, so I'd accelerate at speed like in 4th, but also run out of rpms like 4th......so I think 3.91 it is.

I hope that JC + 3.91 satsifies all my need for speed. I really love my car the way it is, but a little quicker in gear pulls would be cool. I do love the M20's power. Plus, the more I leave that engine stock, the more $$ will stay in my pocket. 8)

You guys know of more 3.91LS, the 325ix?

[AdamF 88iS]

Um, forgot one thing...its in the automatics only, if I remember correctly.

[Bryson]

I do love the M20's power.

hahahaha haha hah ha, sorry had to. Also, what power do you speak of? I can't seem to be able to find it :P

[rwh11385]

I do love the M20's power.

hahahaha haha hah ha, sorry had to. Also, what power do you speak of? I can't seem to be able to find it :P

Don't get me started looking for more power. Just let me be happy with what I got. I'm not trying to race no one. (The HP/torque owns my formercars, and its more fun to drive than a lot of others........)