diff and box ratio help

[EwanBreezy]

I have a 1990 e30 316 with standard open diff
and a m44b19 with original gear box

Ive been told this combination would be crap

I dont know ratios etc of diffs and gear boxes
but could someone help me out with what would be a good diff
to run with that engine and box.

Cheers!

[wellard]

When you say original gearbox is it the e30 box or e36 box?

[EwanBreezy]

Sorry, the e36 m44 gearbox.

[Brianmoooore]

With your existing diff. the engine revs. for a given speed in fourth gear with the E30 engine will be the same as the E36 engine when you are in fifth. You will effectively have lost fifth gear and gained a sub first gear.
To make it work you need a diff. of around 3.3:1.

[jmc330i]

As Brian says, with the E36 gearbox you need a diff with a ratio of around 3.3:1 - the E36 M44 cars use a 3.38:1 diff.
As far as available E30 diffs go, I think you've got the option of a 3.25:1 or 3:46:1. The 3:25:1 ratio will make the car a little sluggish at low revs but it will cruise nicely at motorway speeds. The 3:46:1 would be good for all other driving.

If you can't find a suitable diff, your other option is to use an E30 M40 gearbox (that should be the original gearbox from your 316i and cheap to find), so you can keep the standard E30 diff. The M40 gearbox bolts straight up to the M44 and you can use the standard M40 flywheel, clutch and prop as well.

My M44 E30 runs the M40 gearbox and a 4.10:1 diff which is the best compromise I've found between acceleration and cruising revs. I've also tried both 4.27:1 and 3.91:1 ratio diffs.

[age]

wont he need some spigot bearing to fit the e30 gearbox?
like when doing the m50 conversion?

[Brianmoooore]

He'll need to check that the spigot bearing fitted in the flywheel matches the diameter of the gearbox he's using, and change it if it doesn't.

[EwanBreezy]

I'd rather not change my box tbh

Will try looking for the 3:46:1 diff when I have some money :-/

Cheers for the help