WTB: LSD for 91 535i 5spd. Can i use a 3.15 diff? Will it = better mpg?

[epwebb64]

Prod Date: 10/91. I only ask because my 535i is going to become my long distance commuter. Was thinking a 3.15 LSD might give me better mpg. Isnt it a 3.46 stock diff?

[Spaceturtle917]

Idk about city mpgs, but you should probably get a better highways. I think when i went from 3.91 to 3.43 i went up 1 or 2 mpgs.


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[epwebb64]

I will be driving 300mi round trip every weekend so thats what im thinking.

[ross1]

Your cruising revs will be ~10% less so 2700 @ 80mph instead of 3k. Yeah, I think it should improve highway MPG. You'll probably notice a bit less passing power too.

[GazM3]

Depends on your cruising speed. If at 60mph may be no difference or even worse as the engine rpm is too low putting u in a less efficient rpm range.

Maybe change the exhaust narrowband sensors to get more mpg, and clean your maf with the maf cleaner spray.

[moroza]

Assuming you mean a large-case diff from a 750iL, it won't fit the driveshaft. The boltpatterns for the driveshaft CV and the axles are the same, but the input flange sticks further forward. A driveline shop can shorten the shaft for you to the tune of ~$100-150, and then it'll work.

I switched from a 3.15 to a 2.65 in a 544iT and fuel consumption decreased by ~8%.