Will a 2.9x LSD improve my fuel economy?

[Turf1600]

I just got a new job that is like 22 miles away each direction. I need to improve my fuel economy for obvious reasons. Will a 2.90 LSD help out quite a bit? I'm probably going to do new injectors, fuel filter, cap, rotor, wires, plugs, and an entire new cooling system as well just for good measure.

Any other ideas to help out? The car is a 135k 90 is.

[Stu]

With that rearend, you'll have a 2.36:1 final drive. You may not get better mileage because of the required throttle position to keep roadspeed up.

3.73 is good for mileage -- it keeps the engine at an RPM that doesn't require much throttle and throttle adjustment.

I'd start with pumping up the tires and keeping the weight down.

[Turf1600]

With that rearend, you'll have a 2.36:1 final drive. You may not get better mileage because of the required throttle position to keep roadspeed up.

3.73 is good for mileage -- it keeps the engine at an RPM that doesn't require much throttle and throttle adjustment.

I'd start with pumping up the tires and keeping the weight down.

My tires are all dead even 35. I carry only my backpack and skateboard. I Average 21 MPG combined. I guess I should look and see what LSD I have. What is normally stock in an is?

I wish I had found a 318is instead.

[Jand3rson]

A 325is should have a 3.73 LSD. The 325es had a 2.93 LSD.

[TwoJ's]

It will help significantly on the freeway, but like stated, if you are driving slower than 65-70, you will have to be on the throttle a bit more, and it may not help all that much. Plus, you'll lose acceleration. How's about a 3.25 LSD?

[wickedE30]

Auto or standard......year? Plastic bumper automatic is's have 4.10Lsd's.;)

[Turf1600]

It's standard. And I'm always on the freeway. Aren't 3.25s hard to find?

[TwoJ's]

Yes, they are more difficult. They didn't come on e30's, and I'm not positive what they came on. I think they were on e28's, but don't quote me on that. If they are though, you'd have to swap output flanges and rear cover.

But you'd have to get confirmation on this info, I don't know 100% about that.

[BenM]

My dad has a 3.25LSD in his '89 325i, and I feel that the gearing is slightly too long. The good thing is that it turns 2600RPM doing 80 in 5th, while still being slightly responsive.

If I had done something different, I would have gone for a 3.46LSD. They came later E23's, and '88 528e (Super ETA).

[Turf1600]

Seems like I could just swap out the ring and pinion gears.

[Julien]

i'd say get a 3.46 if you are not doing much city driving.

[Turf1600]

Sounds like a rare diff - but I'll be on the lookout. Maybe I'll just do an s50 instead.

[gobuffs]

A few years ago I went from 15w50 to 5w30 and picked up 2 mpg.

[Julien]

Sounds like a rare diff - but I'll be on the lookout. Maybe I'll just do an s50 instead.

car-part.com look up a 635csi or 528e diff and it'll let you choose the ratio you need.

yes m50 is the best way of getting good mpg out of an e30

[Turf1600]

car-part.com look up a 635csi or 528e diff and it'll let you choose the ratio you need.

yes m50 is the best way of getting good mpg out of an e30

Out of curiosity - what do m50s get?