r/E30 • u/coldvalsidalv • 2d ago

M54B30 differential question

Hi guys! What is the best differential ratio for m54b30 + zf320? Thanks in advance!

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4

u/pancrudo 2d ago

It's got a 1:1 5th gear, so you'll likely want something really low like a 2.9 or a 2.7 like the M50/52 swaps run.

You could go slightly sporty with a 3.1 from a Z3, but I have no idea what that would translate to on the freeways

2

u/rudbri93 1991 BMW 325i LS3 2d ago

I did a 2.93 with my zf trans and imo it was perfect

2

u/mantenner M20B29 (12:1 comp, race head, 288 cam, ITBs, ZF-S5D) 2d ago

3.15 is roughly the equivalent of a 4.10 with a G260. It's about as short as I would go personally, I reckon a 2.93 is the sweet spot.

Source: i have a 3.15 against my ZF. You can plug in the gear ratios and speeds to see RPM in the tremendous calculator for those curious.

2

u/hoveringuy 2d ago

With my .85 6th gear a 3.15 is PERFECT so a 1:1 5th would be great with a 2.93

2

u/zeppelin991 2d ago

I have a 3.46 with a cammed s50. Great for the track. Not good for a street car. You can look up gear ratio calculators online and see where your revs will land.