TECH: Diff swap

[thekid]

I'm looking at swapping my diff to a LSD. I have a 318i, and I've heard that you can swap in a LSD from a 325i (I believe). If thats the diff that I heard about, at 70 mph in 5th I'd be at 4,200 rpms. Has anyone done this swap? or swapped for a different diff? or does any one know the ratios for the different E36 diffs or other diffs that can be swapped in? Lots of questions I know, but this should be an excelent thing, and really help off the line acceleration, traction but lower top speed (which is fine with me).

[Kevin325i]

Model (E36) Stock Gear Ratio
318iS, Ti Manual Transmission 3.45
318iS, Ti, Automatic Trans 4.44
325 Manual Transmission 3.15
328 Manual Transmission 2.93
325/328 Automatic Transmission 3.91
M3 3.0 3.15
M3 3.2 , Auto and Lightweight 3.23


Kevin

[thekid]

um.. thanks, but I was wondering about diffrential ratios, not tranny ratios.... Sorry if I've confused anybody.

[Kevin325i]

Those are differential ratios. Saying manual and automatic is because they gear the auto and manual differently.

Kevin

[thekid]

ah ok. When you said gear ratios at the top, that got me confused. Thanks.

[Kevin325i]

I'm not sure if it's entirely acurate however. I thought the LSD and open differentials were geared differently.

At any rate, PM Autotechnica. He's played around with differntial ratios in his 318

Kevin

[El Presidente]

You cannot swap a 325 diff in a 318 without also changing the driveshaft. I also was interested in a swap, until I leanred the 325/328 diffs were designed differently than the 4cyl engines' diffs. The lengths are different.

[thekid]

hmmm really? I'll have to check into that and see whats possible. Is there another diff that would produce similiar results that you have found?

[El Presidente]

the only diff that would make a difference and would be easy and cheaper is the diff from an auto. Say goodbye to your top speed, but it would make a large impact on acceleration. I wanted a 3.91 for the longest time, but found out the 4.44 was the only one that would work, and those revs are just too high for me.

[thekid]

what kinda revs are we talking about with the 4.44

[thekid]

Also does the whole drive shaft have to be changed or just the rear? I'm still looking into this as a possibility because I'm getting it part and installed in trade for an engine (5sfe from a 92 celica), so as long as the parts would be less than $500 it should be a go.

[El Presidente]

I don't know about the driveshaft, but the revs would probably be around 4 grand at 60-65 in 5th.

[Kevin325i]

PM Autotechnica, he did it with his car.

Kevin

[dutchbmw]

Your car becomes a more bad gas mileage when doing that swap. Is your only reason for doing that a faster acceleration?

[bitcore]

Hey kevin, what does a 98 323is auto fall under? 325?