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burnin oil · 07-28-2021, 08:13 AM

3.73 or 4.10 should be fine on MPG with an OD. Its easier to get rolling and OD cuts the RPM down to reasonable at speed. My personal experience has almost always shown lugging was worse than RPM within reason. Obviously short tires and 5.14 gears with a low RPM motor will be way out of efficiency range on the highway. Low 2000 RPMs seem to work really well for a cruise RPM if the motor is somewhat stock. If you live in a hilly area then a couple of extra RPMs won't hurt.

My old blazer got about the same MPG with 3.07 as it did with 3.73s. A manual trans swap was the biggest help In all the drivetrains it saw. Full time 4x4 to part time. Stock 400sb, built 400sb, stock 350, t350 to sm465. Original was 6 MPG and got a best around 15MPG when built 400sb, 4spd, and part time 4x4. Gear swap was after the stock 350 went in but MPG was constant at approx 12MPG.

07-28-2021, 08:13 AM	#17
burnin oil Registered User Join Date: Jan 2013 Location: Eastern TN Posts: 1,921	Re: Rear end swap 3.73 or 4.10 should be fine on MPG with an OD. Its easier to get rolling and OD cuts the RPM down to reasonable at speed. My personal experience has almost always shown lugging was worse than RPM within reason. Obviously short tires and 5.14 gears with a low RPM motor will be way out of efficiency range on the highway. Low 2000 RPMs seem to work really well for a cruise RPM if the motor is somewhat stock. If you live in a hilly area then a couple of extra RPMs won't hurt. My old blazer got about the same MPG with 3.07 as it did with 3.73s. A manual trans swap was the biggest help In all the drivetrains it saw. Full time 4x4 to part time. Stock 400sb, built 400sb, stock 350, t350 to sm465. Original was 6 MPG and got a best around 15MPG when built 400sb, 4spd, and part time 4x4. Gear swap was after the stock 350 went in but MPG was constant at approx 12MPG.