2.93, 3.25, or 3.73 for S50

[kalib0y]

Still would love to have a 3.25 around though. Do the e34 diffs bolt right up?

[ck_taft325is]

Still would love to have a 3.25 around though. Do the e34 diffs bolt right up?

IIRC, you'll have to swap the gears into a medium case to fit on the E30. Someone correct me if this is blatently wrong misinformation.

[Eric]

Still would love to have a 3.25 around though. Do the e34 diffs bolt right up?

the guts are the same, but the housings are different.

[flyboyx]

this is correct. the ring and pinion are the same in anything medium case. as far as the housing is concerned, i think only e28 is compatible.

my 3.38 is even harder come by than 3.46. instead of spending 600+ dollars on a 97 auto m3 diff, i found a guy in england selling an e34 525ix rear diff for 50bpd. since the housing was no good to me, i had him take the ring and pinion out of it and send only that. i only have about 130.00 invested with shipping from the uk. getting it installed will be another story. i am thinking about reading up on it and trying it myself.

[motors4me]

This.

With my s52+ZF, first I had a 3.25 which was great. Then I wanted to shorten 3rd and 4th up, so I got the 3.46. For canyons and street driving, it made the car noticeably torquier. However, for high way driving, even with my 235/40/17s all around, I'd cruise 80 around 4200.

A week before selling my car I put a 2.93 in because the 3.46 was too rare to give up. I wish I would've run this the whole time. It really is the perfect gearing IMO with the ZF and an s50/2. You can hit 64-65 in 2nd, over 100 in 3rd, and cruise 80 at around 2700! The longer gears give you more time in powerband, making you faster overall.

When Jasper (jahnaboi) and I raced, I could only beat him from a launch. We had almost identical set-ups except he had a 2.93 and I had a 3.46. From 2nd it was about even, then 3rd, and 4th I got pulled on steadily because of all the shifting.

2.93 = better gas mileage, and more usable power.

Quoted for truth and for the 30mpg avg. i get with my 2.93

[mutty]

2.93 for the win. s52+6-speed+2.93= great cruise+ good mileage.

[M3 euro ltw]

sympathy and hate at the same time

I sorta hate posts like this, but I'm sympathetic.

The right answer is really to either write up your own program to do the calculations for each gear based on your tire/wheel diameter, gearbox and redline....

or use one online like Diffsonline has available.

Your needs really determine what diff you choose.

Turbo guys don't want to shift often, so the last thing they'll want is a crazy high ratio diff that forces frequent shifts.

Pure race track mode want to emulate CR as much as possible since most pure race engines have a narrow powerband, and you need to stay in it.

DD may place fuel economy high on the list, and want an underdrive gear too (ie 6 speed needed) to balance a "fun" diff for the first 5 gears.

Example: My race car: Euro 6 speed, 4.45 diff. Turns gears 4,5,6 into a real CR gearbox. I NEVER use second on a race track, and the gap from 3 to 4 is not objectionable, though it is larger than the other two gaps.

So, figure out what your top speed is required, and match that to your redline/wheel/tire package and tolerance for whining on the highway between track days.

(for example, a 3.91 and typical 1:1 5 speed might be perfect if you don't have any Loooong tracks for high speeds...again, redline and tire package make a difference)

[e30polak]

2.93 for the win. s52+6-speed+2.93= great cruise+ good mileage.

With a 6 speed I wouldn't go any longer than a 3.46.

[funcrew]

S52 with ZF (non-overdrive) trans and 3.25 diff (now puked). As a daily driver, it's little too short for comfortable freeway cruising. A 2.93 would be better for traveling, and that's what's going in next.

[mutty]

With a 6 speed I wouldn't go any longer than a 3.46.

Until you drive such a setup

[MattM]

i have to agree, my daily commute is 35min each way(not including any traffic) and i love the zf320 + 2.93 for this.... if and when i stop daily driving the car, i think id get a 3.25 or something just for a little more torque in the lower RPM's

[e30polak]

Until you drive such a setup

I have and it's pointless IMO. The only reason to get a 6 speed IMO is to run fairly short final drive gears, while still cruising at low revs in 6th on the highway. Gas mileage is always cool, but not worth the extra money for the trans IMO. I'd rather run a 3.25/3.46 with a getrag 260 for gas savings.

[brn2ply7]

What about the plentiful 3.07 gear as a little bump up from the 2.93 for a daily?

[phreshkid]

What car does the 3.07 come from? I have a deal on a 2.8litre z3 with a 3.15s that a guy is selling. I just want something in between a 2.93 and a 3.25 since I'm running the zf as well.

[RoadHazard]

I'm using 3.15 with the 5-speed ZF right now but I haven't driven the car much so can't tell if it's too short at the moment.