Gear ratio comparison...

[7pilot]

Yeah, thats what I'm thinking. My motor is real torquey. What do you think of rebuilding a diff. Taking 2 diffs to create the 3.25 instead of buying a used one with an unknown history? I can get one built for 500 out the door. bench test the lsd (will determine strength but not how long it will last) replace the seals , os bearings is bearings gasket, shims etc

It depends on the configuration of the majority of the tracks you run on.

I think the best all rounder would be the 3.25, if you can handle the torque output on a short twisty wet track.

The 3.46 may pull revs too quickly for a nice even surge of torque.( car pulls in short bursts sort of like a kangaroo eta)

You'll need to compare your torque output maps to gearing maps of the diff/gearbox combos to find the driveline spec that will allow you to exploit the meat of the torque for the longest amount of time/distance.

m

[Wh33lhop]

What tires (size) do you run?

fyi my tire size is 225 50 15 for any calculations. Thanks in advance.

I'm considering yanking my S3.73 and rebuilding it.

[etxxz]

500?!
i believe bma has a rebuild/shim kit. I'll take what you have and do this. If you don't know about how to set the backlash properly then i can see how 500 for a diff AND the rebuild make sense. You can always sell your current one to offset the cost.

Different strokes for different folks. I liked my 3.25 better in 1st and 5th better, but that's it. I wanted to shorten up 3rd and 4th, because I felt they were TOO long. Overall the 3.46 is a much better gear for street driving and canyon runs. The 3.25 maybe better around the track and for drifting however.

2.93 for drifting.. atleast with an s52 and above power levels. the 3.25 is just good all around. Maybe tight canyon runs, like you say, a 3.46 will have its use. I do think 4th is a bit long. A lot of folks on bimmerforums run this gearin. What tires (size) do you run?

[RedDotRacer]

i think that too short of a gearing on a reasonably torquy motor like ours is stupid because you'll be shifting all the time instead of being able to use your gear through and out of a turn. A 3.25lsd is perfect for a ZF IMO (i'm also running 235/40-17 NT-01's), its short, but not too short. I use 2nd gear to take off on the street. With this setup there's one 1 turn i've ever needed to shift mid-turn and that's because its a double apex... and i think i'm faster through it if i just use the taller gear (4th)

Yeah, thats what I'm thinking. My motor is real torquey. What do you think of rebuilding a diff. Taking 2 diffs to create the 3.25 instead of buying a used one with an unknown history? I can get one built for 500 out the door. bench test the lsd (will determine strength but not how long it will last) replace the seals , os bearings is bearings gasket, shims etc

[e30polak]

i think that too short of a gearing on a reasonably torquy motor like ours is stupid because you'll be shifting all the time instead of being able to use your gear through and out of a turn. A 3.25lsd is perfect for a ZF IMO (i'm also running 235/40-17 NT-01's), its short, but not too short. I use 2nd gear to take off on the street. With this setup there's one 1 turn i've ever needed to shift mid-turn and that's because its a double apex... and i think i'm faster through it if i just use the taller gear (4th)

Different strokes for different folks. I liked my 3.25 better in 1st and 5th better, but that's it. I wanted to shorten up 3rd and 4th, because I felt they were TOO long. Overall the 3.46 is a much better gear for street driving and canyon runs. The 3.25 maybe better around the track and for drifting however.

[etxxz]

i think that too short of a gearing on a reasonably torquy motor like ours is stupid because you'll be shifting all the time instead of being able to use your gear through and out of a turn. A 3.25lsd is perfect for a ZF IMO (i'm also running 235/40-17 NT-01's), its short, but not too short. I use 2nd gear to take off on the street. With this setup there's one 1 turn i've ever needed to shift mid-turn and that's because its a double apex... and i think i'm faster through it if i just use the taller gear (4th)

[RedDotRacer]

Don't mean to bump an old thread, but I'd like some more info on this subject. I'm getting ready to put a zf tranny into my e30. My motor is an MM 3.2l stroker putting out about the same power as an s52. Which diff would you reccommend?

choice between 3.25 and 3.46. Mainly a track use car. After running the gear ratio calculators looks like the 3.25 is the most similar to a 3.73 to the getrag 260. and the 3.46 would be somewhere between a 3.73 and 4.10 on the getrag 260 (1st was non existent).

I have had a 4.10 on the getrag and that it was way too short. The 3.73 worked well and is what I'm leaning towards, but I've never felt a 3.46 equivalent.

For people with about the same power which diff do yo prefer?

fyi my tire size is 225 50 15 for any calculations. Thanks in advance.

[e30polak]

I should be rolling down through LA with my E30 later this year. We should do some pulls.

Sounds good. I'm down to lose to you. ;)

That gearing must be monstrous! I definitely want to get a ride with that 6 speed in there!!! :D

I could get a bunch of people together to have some fun pulls with! :up:

[jrdeamicis]

I should be rolling down through LA with my E30 later this year. We should do some pulls.

[jrdeamicis]

We speak each other's language lol. Get some video footage of this beast in action! I need some inspiration to keep my boost dreams alive! :D

The hard part is getting the money to do so!

Of the E30 or the M3?

The money is always the hard part.

[e30polak]

Now we are talking.

We speak each other's language lol. Get some video footage of this beast in action! I need some inspiration to keep my boost dreams alive! :D

The hard part is getting the money to do so!

[jrdeamicis]

I meant with an an rms aftercooler and custom tune. ;)

Now we are talking.

[e30polak]

For 3Gs you can have a new blower. :)

I meant with an an rms aftercooler and custom tune. ;)

[jrdeamicis]

I'd rather buy a used blower. ;)

Thanks for the offer though! :D

For 3Gs you can have a new blower. :)

[mazur]

Here you go...3.46 with 245/45/16 tires


Gear Mph per 1000 RPM Mph @7000 RPM Mph @7000 RPM
--------------------------------------------------------
1 5.02 35 35
2 8.45 59 59
3 12.71 89 89
4 17.25 121 121
5 21.22 149 149



Gear Change RPM drop (change @7000) RPM drop (change @7000)
-------------------------------------------------------------
1 -> 2 -2846 (to 4154) -2846 (to 4154)
2 -> 3 -2343 (to 4657) -2343 (to 4657)
3 -> 4 -1844 (to 5156) -1844 (to 5156)
4 -> 5 -1309 (to 5691) -1309 (to 5691)