Quote:
Originally Posted by Big Dave
Overall gear ratio is a powerful tool for improvement of MPG. Too bad so many vehicles are so difficult to effect gear ratio modifications.
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Both of those are very true. There are 2.79 BMW diffs out there that would fit my car, but I don't think I'd want to go that low; I do know a guy who did such a swap for a 2,000-mile trip, though.
If the fasteners aren't damaged or crudded up (i.e. undercoated or rusted), even a novice can do a diff swap on a BMW in a couple of hours. Even better, junkyard diffs go for less than $100 and are nearly always in great condition (not necessarily so for the limited-slip clutch plates, but those aren't hard to replace).
Interestingly, I'm having to drive a bit faster to get better MPG with this diff. I used to be able to do 40 MPH in a 45 zone in 5th gear, but now I have to do 50 in order to not lug the engine or hunt on/off the throttle.