What ratio is my diff?

[RiggsyB]

I've got a 1995 E34 UK model 520i Touring, with a 5 speed manual transmission (1:1 top gear I believe)... The gearing seems a tad short for me, for what is essentially a cruise car (i'm not pretending it's a quick car), cos 85mph in top gear equates to 4000rpm! The same as my mates E36 compact 316i!!!

Now, i want as good economy as possible from this car, and am probably even going to gas convert it at some point. So what diff ratio have I got, and could i fit a slightly taller one from a slightly larger engined 5 series to drop the engine revs for motorway driving a tad?

Or, what about the 6 speed manual box even?

I appreciate that this is probably a quite drastic approach to potentially saving about 2 to 3mpg on a run, but hey... I'm new to this... And never realised that all the 5 series engine variants came with so many diff ratios! I mean, the 1995 E34 540i/6 that my dad had years ago was geared for interstallar space travel... At 150mph on the German Autobahn it had barely registered 4000 revs in top!!!

[Blitzkrieg Bob]

upper corner of the rear of the diff case.

This tells you the ratrio, and if it is open or LSD.