Diff ratios

[Cheyne_Oo 1]

Im just wondering if any one could tell me what diff ratio I need for my manual conversion. I have a e36 328I and using a 325 getrag box i havent look into the gearing side of things, all I know is the auto diff makes the engine rev its guts out at 100km, so if anyone can give me an idea or even have one for sale of what I need it would help heaps.

[BM WORLD 1283]

factory 328i manuals went with a 2.93

325i used a 3.15 ratio

but there are also 3.07

I have 3.07 and 3,15 diffs in stock

021433600

[email protected]

[Ahmedsinc 414]

3.07 & 3.15 will give the most economical fuel figures. 3.46 will give you a nice bump in acceleration but come at a cost to efficiency and top speed. 2.93 is too tall IMO. 3.23 however is my pick for standing acceleration, overtaking and not being impossible at 60mph.

3.07 would probably be fine with the extra torque of the M52

[BM WORLD 1283]

I use a 3.15 in my 328i about 2650rpm at 100km/h in 5th but I think I would change it if I could be bothered to a 3.07 about 2550rpm at 100km/h in 5th

[Allanw 1071]

..... and not being impossible at 60mph.

You're trying to rark up Ron, right?

[allan 295]

In the compact now have a 3.15:1 M54 b25 does a shade over 2500 at 100k 5th gear 1:1. It did have a 3.48:1 and first was useless and revved at about 3100 at 100 if that is of any help.

[Ahmedsinc 414]

You're trying to rark up Ron, right?

Moi? Facetious?

Never!

[Rubix 434]

Necrobumping this thread.
Converting my e36 328i shortly (aiming for this weekend).

Jatco auto, likely has a 3.91 diff (as this was the factory diff for a 328i auto, but the tag is missing on mine), replacing with ZF 5 speed. From what I understand i'll likely be sitting at 3400ishRPM in 5th at 100kph with the 3.91, while I wouldn't mind this for a couple of weeks I'll likely want to have somewhat decent fuel economy in the future.

I take it I'll need a medium case diff? Brent, do you happen to have any 3.15's or 3.46' in stock? Pricing?

Actually using a diff ratio calculator..

25 inch diameter tyre (rounded up from 24.972) - (225/45/17 tyre on 17" rim)
3.91 diff ratio
62mph/100kph = 3258rpm? Surely this can't be right? Seems awfully low rpm, I'd almost be happy with it if that's the case o.o

Edited September 17, 2015 by Rubix

[Ahmedsinc 414]

Cruising revs don't tell the entire story. 3.91 final drive will turn your 5 speed into a 4 speed as first gear will be uselessly short. Unless you do a lot of burnouts, in which case stick with the 3.91 Given the M52B28 develops ok torque I'd look for a 2.93 or 3.07, definitely wouldn't bother going higher than 3.23. M50s benefit from the shorter gearing to mask our lack of bottom end torque, not so much of a problem for the B28. Yip, medium case is what you need. Complete pain in the ass job but it utterly transforms the car, you won't regret the swap

[BM WORLD 1283]

328i jatco auto , normally a 3.46 diff

3.07 will do nicely

call me 021433600

http://members.dodo.com.au/~wawawa/revs.htm

[Rubix 434]

328i jatco auto , normally a 3.46 diff

3.07 will do nicely

call me 021433600

http://members.dodo.com.au/~wawawa/revs.htm

It's an e36, are you sure it came with a 3.46? Can't find anything anywhere to support that.

EDIT: Actually you may be right..According to this: http://www.driftworks.com/forum/technical/42834-bmw-e36-differential-ratio-got-screwed-up.html Jap 328i's have a 3.46? this definitely correct?

Edited September 17, 2015 by Rubix

[BM WORLD 1283]

std spec for that type

http://bmwfans.info/parts-catalog/E36-Cabrio/Europe/328i-M52/R-A/1996/browse/rear_axle/rear_axle_drive/

wrecked about a million of these cars , and that's what most of them have , unless they have been swapped out etc

a lot of other info out there relates to usa spec ...