Looking to get a longer diff on my e30 m3

[m3j0n]

what are my options if I want to stick with a factory LSD that fits in an e30 m3 and can accept an mcoupe finned diff cover?
my factory diff is a 4.10 and its way too short with my 95 m3 s50/zf swap. What LSD ratios were offered from the factory that I should consider? Thanks!

[FredK]

You have a ton of options.

Any Z3M diff will bolt right up, and get you very close to the gearing of a Z3M. Because the E30 tire diameter is smaller than a Z3M's, the effective ratio will be slightly higher.

So, a 3.15 or 3.23 from a Z3M will work. An E28 3.25 or 3.46 LSD will also work with the finned diff cover. If you want a nice low diff ratio, you can get a 2.93 from a 325e.

[m3j0n]

You have a ton of options.

Any Z3M diff will bolt right up, and get you very close to the gearing of a Z3M. Because the E30 tire diameter is smaller than a Z3M's, the effective ratio will be slightly higher.

So, a 3.15 or 3.23 from a Z3M will work. An E28 3.25 or 3.46 LSD will also work with the finned diff cover. If you want a nice low diff ratio, you can get a 2.93 from a 325e.

is a z3M diff any different from a standard e36 diff, for example one from an e36 m3? Which year z3M had a 3.15 vs 3,23?

[FredK]

Yes. The Z3M has the same case-style as the E30 (and E28/E24/E23). It is incompatible with the E36 diff.

The S54 Z3M had a 3.15. The S52 Z3M had a 3.23.

[m3j0n]

ok, cool.. thanks... I don't think Ill be finding a 3.15.. that must be ultra rare.

[MR 325]

A 3.25 ratio is just about perfect for that engine and trans combo.

[m3j0n]

yeah.. trying to find one now... they are either priced high, or sold....:(

[ajhostetter]

Looking to get a longer diff on my e30 m3

Wanganstyle (on here) builds 3.15 torsens for the E30. I just picked one up. PM him. He knows rear ends and can build pretty much anything.

[e30rapidic]

I have an S3.25 with my S50/zf, best all around ratio i've tried. S3.46 was great fun but too many rpm's. S2.93 is great for cruising but sucked a bit of the fun out. It is a toy after all.

i'm building a 3.15 now, got the gears from an e36

[lukeADE335i]

The 3.25 LSD is common in the e28 535i - that's where I got mine from.


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[m3j0n]

Wanganstyle (on here) builds 3.15 torsens for the E30. I just picked one up. PM him. He knows rear ends and can build pretty much anything.

Probably more pricey than sourcing a used diff though, right?

I have an S3.25 with my S50/zf, best all around ratio i've tried. S3.46 was great fun but too many rpm's. S2.93 is great for cruising but sucked a bit of the fun out. It is a toy after all.

i'm building a 3.15 now, got the gears from an e36

AWESOME info! Thanks for being the guinea pig!! LOL.

The 3.25 LSD is common in the e28 535i - that's where I got mine from.


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cool. thanks.

[Wanganstyle]

Probably more pricey than sourcing a used diff though, right?




AWESOME info! Thanks for being the guinea pig!! LOL.



cool. thanks.

Much more but new everything is just that

If you have a rear end shop local to you that knows BMW units they can just re-configure your original differential from 4,10->3,15. Lots of labor to expense.

I always fit the late model E36 gears as they are a updated more efficient design than the earlier e28/34 gears. Some won't care about this; BMW revised gears for efficiency mid 90's and then again late 90's in the e38/39/46

[agent]

For the ZF gearbox, 3.15 is the perfect ratio for street/highway driving with some AutoX and/or track days sprinkled in.

[lukeADE335i]

I always fit the late model E36 gears as they are a updated more efficient design than the earlier e28/34 gears. Some won't care about this; BMW revised gears for efficiency mid 90's and then again late 90's in the e38/39/46

Any idea how much difference to economy would this make? Always interested in making the car better on fuel. :)



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[Wanganstyle]

Any idea how much difference to economy would this make? Always interested in making the car better on fuel. :)



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very difficult to quantify this; a gearing change will be much easier to compare.

Fuel data for Average combined Fwy/local driving (prior DD's)

1998 M3 3,23->3,46 = decrease 24-25 MPG to 22-23 MPG
2003 325i 3,15->3,46 = decrease 25-26 MPG to 23-24 MPG
1992 525i 3,23 ->3,15 = increase 23-24 MPG to 24-25 MPG

the more modern m54 engine with is double vanos and can bus electronics is much more conservative on fuel on freeway cruising; its 29-30 mpg.
Obviously 3200cc vs 2500cc is another issue regarding mpg.

Choose the final drive that suits your desired MPG for the kind of driving you enjoy. Stock BMW is always good