3.38 z3 diff

[heathy325]

Just after a diff to put in my e30 I've got the m52 in with the 2.8 gearbox and just after info on the best ratio diff, Is the 3.38 one a good choice of shall I keep looking for a better ratio one? If so what's the best to get

[rich318i]

2.93 was standard with that box.

3.07, 3.15, 3.25 is what most like to use.

I use the 3.25 myself and love it

[Motorhole]

Might be slightly short - but would be perfect for track use! If you give me your wheel/tyre sizes I”˜ll plug the numbers into a spreadsheet I made up - tht will give you a rough idea of the speeds you”˜ll have in each gear at a given rpm

[ashje]

Might be slightly short - but would be perfect for track use! If you give me your wheel/tyre sizes I”˜ll plug the numbers into a spreadsheet I made up - tht will give you a rough idea of the speeds you”˜ll have in each gear at a given rpm

That sounds interesting, i'm in the same dilemma at the moment.

I will be running 17's, lowish profile tyres, i was thinking along the lines of running a z3 diff given the bigger wheel

[leeparkes]

Wont the 3.38 be a small case diff?

[heathy325]

That's what I thought and the majority of them are but I've found a few that are med case! I'm running a 3.91 at the min and running the standard 15" cross spoke bbs with 205/50/15 tyres

[DanThe]

Will be way too short for road use

[Brianmoooore]

Will be way too short for road use

Equivalent of running a 4.17 diff. A 2.8 M52 requires longer gearing than a 1.6 E30 saloon!

[Motorhole]

Heathy325 - with those wheel/tyre sizes, 70mph in 5th will be approx. 3500 rpm. Redline (6500 rpm) in fifth will be about 125mph. Will need 2 changes to get to 60mph (won't do 60mph in 2nd gear, unless you can rev to 7500rpm!).

Ashje - with 215/45/17 wheels/tyres, about 3250 rpm at 70mph in 5th. So < 10% lower than the figures I've quoted about for Heathy325. You would still need 2 changes to get to 60 mph.

Edit: There's a 3.07 Torsen diff in the for sale section right now, which would be perfect. JUST about hit 60mph at the top of second gear, 70mph at about 3100 rpm in 5th.

[HairyScreech]

A 3.15 is about the same as having a 3.91 with E30 overdrive box.

[heathy325]

Thanks for that so ideally I need either the 3.07 or will a 3.25 be ok?

[Brianmoooore]

3.25 is the equivalent of 4.01 in normal E30 terms. You'll still have a top gear of four and a half, rather than fifth.
3.07 equates to 3.79, which is the top end of the right area.

[heathy325]

Is it possible to swap the internals from the e36 diff into An e30 casing?? If so I have a 2.93 e36 diff available

[rich318i]

yes you can

[HairyScreech]

Beware the E36 diff being a large 210mm case from an M3.

You need a 188mm medium case.

But yes the units will swap from one diff to another.

If you change the spool/lsd unit and leave the gears with the case then that's easy, swapping crownwheels and pinions between cases requires new crush washers and back lash adjusting.

[ashje]

So can i buy an open medium case 3.25 e30 diff and a medium case e36 lsd of any ratio.

Then put the spool/lsd unit from the e36 lsd into the e30 diff and i'm good to go?

[heathy325]

In theory yes, after some digging around I've been told the internals from the e36 will fit in the e30 case providing there from the 188 type diff!!! I'm currently in the process of this I have an e30 3.91lsd and a 2.95 e36 open diff and going to make a 2.95lsd to fit the e 30 so will let you know how it goes

[HairyScreech]

In theory yes, after some digging around I've been told the internals from the e36 will fit in the e30 case providing there from the 188 type diff!!! I'm currently in the process of this I have an e30 3.91lsd and a 2.95 e36 open diff and going to make a 2.95lsd to fit the e 30 so will let you know how it goes

Yes to the above, the internals should fit but you will find that swapping the actual gearing between the cases will need proper fitting and backlash setting.

If you wanted to fit the LSD to the 3.91 and make a 3.91 LSD then that is much more simple, just unbolt the crownwheel from the LSD unit and fit the 3.91 crown wheel and LSD unit back into the 3.91 diff.

My suggestion here would be to get a medium case open 2.95 that fits an e30 and put the LSD unit into it or just get a whole 3.05 3l Z3 diff.

Fitting the gears from the E36 case into the E30 case is the hard way to go about this one.

[heathy325]

I'm after the 2.95lsd but can't get one I can afford, so I'll d the swap I've done diff builds before with new crush washers and backlash settings and with a bit of patience was fair easy for me, will post picks when I'm done