3.09:1 diff

[dickkark]

I need a diff that will take 400 hp is small in overall size (smaller than the TVR behemoths,say e36 bmw size)
and roughly 3.09/3.1:1.
any suggestions?

[Busa_Rush]

BMW 5 series E34 525 TD or 530/330 auto are about that, there's also a 2.56:1 in the 3/525 TDS if you fancy running lower Some of the 5/330's also came with LSD.

[GavinPearson]

You are going to run into problems simply because the teeth will not be able to take the torque. Typically the pinion teeth will fail through fatigue even when using ground gears.

For a production car you would realistically need an 8.5" crownwheel on a manual car, on an automatic where a torque limiter can be applied to the engine it could just scrape by on an 8" diff (old XK8 / XJ8). If you want to go smaller then a 7.5" diff would be extremely marginal, even if you got the gears shot peened.

What is the application?