Which diff should i use?

[M-technik-3]

http://www.bimmerfest.com/forums/showthread.php?t=5078&highlight=46+diff+ratio

Came in automatic/steptronic equipped cars...

[1990m3]

My 3.46 came from a e28 528e

My 3.23 came from an M Coupe

[redmist]

With approx 400hp and a zf trans with a 1:1 5th gear, a 2.79 with three clutches works for me.
A e36 diff will work or a large case diff will work with some relatively minor welding/fabrication to the rear crossmember. I put an e36 diff in my ls1 e21 as well as an Audi torsen diff ($50 from a junkyard and indestrucable)in an e12. All depends on how much work you want to do.

[flyboyx]

Correct, the Z3M and Z3 M coupes had 3.46lsd Torsen style diffs.

3.46lsd are found in E23 7 series. I have two now one behind a s50 powered e30 and the other in a dog legged M3.

mz3's came with a 3.25lsd. that is also what came in my parts car.

[e30polak]

how is that possible when i had a 4.10 and @ 85 i was @ 4k...makes me scratch my head.

With the zf trans, it's (1.24:1) 4 th gear, and (1:1) 5th. That makes it a higher overall final drive. ;)

[e30Rob]

3.25 all day long. Im using a 3.73 and i hate it. About 4100RPM at 80

how is that possible when i had a 4.10 and @ 85 i was @ 4k...makes me scratch my head.

[Uber E30]

i would be using the zf 95 m3 tranny and was debating on 3.25 3.46 or the 3.73

3.25 should be the highest you go for anything that sees alot of highway.

[Uber E30]

Correct me where I'm wrong.

This is assuming U.S. market cars.

5spd 325is all years: s3.73
Auto 325is thru '89 model year: s3.73 should be 4.10
Auto 325is '90: s4.10
5spd/Auto 325i thru '89 model year: 3.73 with limited slip option auto should be 4.10
Auto 325i '90-'91: 4.10 with limited slip option
5spd 325i Sport Package '91: s3.73
Auto 325i Sport Package '91: s4.10
5spd 325iC all years: 3.73 with limited slip option
Auto 325ic thru '89 model year: 3.73 with limited slip option
Auto 325ic '90-'92: 4.10 with limited slip option
5spd 325iX 3.91 (VC LSD)
Auto 325iX: 4.10 (VC LSD)
Auto/5spd 318i until November of '83 build-date: 3.64 with limited slip option
Auto/5spd 318i after November of '83 build-date: 3.91 with limited slip option
318i/is '90-'91: 4.10 with limited slip option
318iC '90-'92: 4.27 with limited slip option
E30 M3: s4.10
5spd/Auto 325/e/eS until July (?) of '85 build-date: 2.79 with limited slip option
5spd/Auto 325/e/eS after July (?) of '85 build-date: 2.93 with limited slip option

E30 M3 and all 6-cylinder cars use a type 188 diff
M10 and M42 cars use a type 168 diff

[M-technik-3]

Went oversized to smooth out potholes in the NorthEast Or roads are no better than cow paths these days.

Yes some of the steptronic and 3.0 cars had 3.46 torsens. Depends on the year basically. I have a pdf of the factory manual for the 3.46 but can't find it at the moment.

[Stu]

Correct, the Z3M and Z3 M coupes had 3.46lsd Torsen style diffs.

3.46lsd are found in E23 7 series. I have two now one behind a s50 powered e30 and the other in a dog legged M3.

I thought the MCoupe came with a longer rearend? According to this article on AxisOfOversteer, AC says his S54 MCoupe had a 3.15. He replaced it with a 3.46 from an E24.

http://axisofoversteer.blogspot.com/2009/08/whats-difference.html

I believe '88 528e (Super E) Automatics have a 3.46 also (Unsure on limited-slip).

I agree that with slightly oversized tires, 3.46 is a great gear for a 1:1 'box in a 24v E30!

[M-technik-3]

I have the same gearbox and 3.46 love it. It's about 3600 at 80mph with oversized tires.

[mattdk318i]

3.25 all day long. Im using a 3.73 and i hate it. About 4100RPM at 80

[Strickly German]

i would be using the zf 95 m3 tranny and was debating on 3.25 3.46 or the 3.73

[M-technik-3]

The gearbox is your other determining factor. As is your tire size. Over or Undersized.

[Strickly German]

what do you think thes50 with 3.73 will range in 5th gear at 70?