M50 + zf 320+ 373 diff= no highway

[mazur]

My '69 Chevelle SS had a 3.91 diff and a big block, and obviously no overdrive. Brutal on the freeway, 8mpg or so. This was normal during the muscle car era, nobody thought anything about it.

No overdrive, eh? So what was your top speed, 80mph? lol.

[e30 blue]

Hi Matt T , 4th not 5th? So it looks like I need to buy a used diff to let the car run freely on the road.

[87e30]

Personally, I'd go for a 3.46 if I was in your position. BUT, fi highway mileage is a concern for you the 2.93 would be best on gas, with the 3.23 (whatever it is) as the best compromise.

[WADE30]

I get 25-28 MPG and I have a 3.25

[jrdeamicis]

2.93 or 3.25

I would not mind a 3.46 even without the 6 speed. The drive ability is worth it.

[e30 blue]

So most of the dudes here with the same set up are running 2.93, 3.25 or 3.46. Well I am going to go look for one. It will probably come down to what's available of the 3 mentioned here.I am leaning toward the 3.25 because I cruise so much on the freeway.Thats just how I roll.

[Bimmerman325i]

if you're concerned with highway fuel mileage, 2.93 or the rarer 2.79 for sure.

[MattM]

Hi Matt T , 4th not 5th? So it looks like I need to buy a used diff to let the car run freely on the road.

4th :D get about 27 mpg

[e30 blue]

Went and took a look at a 90 535 and a 85 535 .The diff in these look different than our e30's. What is up? Do I need to swap the member out?

[rneedham1979]

I have a 2.93 and roughly 3400-3500rpms @ 80mph

[Jean]

Went and took a look at a 90 535 and a 85 535 .The diff in these look different than our e30's. What is up? Do I need to swap the member out?

I don't think an e34 diff will work, the e28 diffs will though. You swap the rear mount and output flanges.

[e30 blue]

Thanks Jean, Now, can I live with a diff without LS.I looked up the 85 e28 and it has the 3.25 gear set, so that might be the one for now. From what I was able to gather , not many e28 cars came with the LS diff.

[Uber E30]

Tons do man, i see them at pick n pulls all the time. I will PM you next time i see one.

[mazur]

Don't get a 2.93. Your car will feel very unresponsive and slow.

[e30 blue]

Today was a good day. Thanks Uber e30,I took your info and went to (pick and pull) and sure enough I found a 535 with 119,000 miles and it had a big "S" on the diff . So the gear is 3.25. The oil that was in the bottom was golden. Can't wait to get this in the car, so I can get a highway pass.