I'm considering swapping rear differentials in my car.

I understand that my '83 240D, has a 3.69 differential in the rear. My top speed is about 80 mph without roof racks, its about 75 mph with a 4-bike+faring Yakima roof rack on top.

Switching to a lower number rear differential would reduce my top speed a bit, but also reduce the amount of fuel consumed, lower RPMs at cruise, etc. and result in increased fuel economy.

What would you guys say to a 3.08? What would you say my top speed would be, and what might I see MPG-wise?

Currently, top-speed of 75 mph is "nearly" WOT for me...although, I assume its not really consuming much more fuel because the engine can only spin so fast after all. Lower RPMs even at WOT = lower fuel consumption right?

Thanks in advance for the advice.

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1983 Mercedes-Benz 240D
Automatic, A/C, Power Sunroof, Power Right Side Mirror
231K Miles FOR SALE MAKE OFFER