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Old 04-09-2009, 10:05 AM   #8 (permalink)
Shawn D.
Harebrained Idea Skeptic
 
Join Date: Jun 2008
Location: Alpharetta, GA
Posts: 211

The White Car - '84 Mercedes-Benz 300td
90 day: 28.84 mpg (US)

The Blue Car - '86 BMW 535i
Last 3: 23.86 mpg (US)
Thanks: 19
Thanked 13 Times in 9 Posts
Quote:
Originally Posted by Big Dave View Post
Overall gear ratio is a powerful tool for improvement of MPG. Too bad so many vehicles are so difficult to effect gear ratio modifications.
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.
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Last edited by Shawn D.; 04-09-2009 at 10:12 AM.. Reason: Spelling correction.
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