Hi all

Just want to get my head around diff ratios.

I would like to know what diff would be in a genuine 87 740 turbo with a m46?
I own a 87 740 turbo with a m46 which i converted from a AW70 i currently has a 3.73 diff.
on the weekend i drove a genuine 87 740 turbo with a m46 with an unknown diff ratio. and made my car feel like a granny scooter.
Both my car and the one i drove on the weekend and setup the same, both have turbo+, same cam, etc.
The only difference i know of is my box is the older cast iron. and the other alloy, and both have roughly the same k's

the person who owns the car said this is mostly likely due to my car being setup for auto and the diff ratio being wrong.
When driving my car the car has a habit of reving out very fast without much pull, whilst the other revs steadly and pull like a dog with a golf ball up its arse.

please could someone shed some light on the problem, could there be something else i am missing, clutch?? gearbox ratios?? etc.