m20b20 diff swap

[ForcedFirebird]

With you having a b20, I would suggest go ahead with the 3.91. You won't lose a lot of acceleration, but you will have better fuel economy and only slightly lower RPM at speed.

Use this calculator to see you various speed/RPM differentials when swapping gears...

http://www.csgnetwork.com/rearendgearcalc.html

[ciocc]

you may like the 3.25 ratio differential. In my e30 at 135kph I am turning 3000rpm. makes the car a 4 speed with a true overdrive feel, much like an old school car

Won't the acceleration suffer? It's already kind of slow when starting to move

[5Toes]

you may like the 3.25 ratio differential. In my e30 at 135kph I am turning 3000rpm. makes the car a 4 speed with a true overdrive feel, much like an old school car

[ciocc]

Hello everyone, first time posting here, so please correct me if i'm posting in the wrong sub-forum.

My car is an '89 320i with an m20b20 engine. The diff has been humming for quite a while and i decided it is time for a change. My current diff is an open 4.10 and driving at about 100 km/h i get around 3k rpms which is kind of high imo. I was thinking about a 3.91 swap. Is it worth swapping it? Would i get significantly lower rpms at higher speeds? I mainly do city driving but would like to go on longer trips in summer