In these days of high priced fuel (especially the premium I need for my EAT chip), I think I'm willing to sacrifice a little zip in my 1991 535i in return for better fuel mileage. My car was built in 10/90, so I'm not sure if it has a 3.91 ratio (1990) or a 4.27 ratio (1991). At any rate, the manual trans equipped cars had either a 3.46 ratio in the 535i and 3.23 ratio in the 525i. I'm figuring changing to one of these diffs hopefully should move me from my 23 mpg interstate mileage up to 25-27 mpg. The only real question is whether it's a straight swap or not. Anyone out there know if I'll encounter any problems if I do this? I've been told I wouldn't have to do anything in regards to the speedometer because the sensor is in the diff. Is that correct too? Any help would be appreciated.

Grace and peace,

Robert K
1991 535i