What diff should I run in my E30?

[JoshG]

I have an E30 with a 328 engine and box. What diff should I run to get the best performance?

I will be going to the ring so don't want it to top out at like 120 but equally don't want stupid long gears.

Any help would be appreciated.

[daimlerman]

Are you using the ex E36 gearbox with direct drive 5th?

If so,you need a diff with a ratio around 3:1 or 3.15:1.
Unfortunately,these only came in E30 fit on M3,so are both rare and expensive.

All is not lost,though,because some E28 models have suitable ratios,but will need a backplate swap to suit E30.

[jmc330i]

If so,you need a diff with a ratio around 3:1 or 3.15:1.
Unfortunately,these only came in E30 fit on M3,so are both rare and expensive.

All is not lost,though,because some E28 models have suitable ratios,but will need a backplate swap to suit E30.

Z3M diffs are 3.15:1 LSDs and are a straight fit in an E30 once the output flanges have been swapped for E30 ones.