Differential from 316 with swapped internals?

[Polski Drywer]

Hello there. I've searched the forum and online but found a lot of "don't do it" answers for this question. I have a 316 with m40 motor but am planning for some more power lets say. Where I live e30 differentials are HARD to find or SUPER expensive. I don't have the car yet but, I'd still want to get some plans ready for it. I'm guessing 316 will have a smaller differential than an m20 car? If so, is there a chance to swap internals from a 'small case' e36 to make it work?

I'm always up for a challenge, or for a shop to have a challenge ;) It's winter here and due to my limited garage space, doing 'internal work' is all I can do for now. Internal work will change the cost from more than 4500zl to 550zl for the parts alone.

Can anyone give me a link to a previous thread or just to highlight if what I said is correct, wrong or possible?

Thank you.

[tomstin]

This may give you something to think about. https://www.e30zone.net/e30wiki/index.php/Differential

[82eye]

Hello there. I've searched the forum and online but found a lot of "don't do it" answers for this question. I have a 316 with m40 motor but am planning for some more power lets say. Where I live e30 differentials are HARD to find or SUPER expensive. I don't have the car yet but, I'd still want to get some plans ready for it. I'm guessing 316 will have a smaller differential than an m20 car? If so, is there a chance to swap internals from a 'small case' e36 to make it work?

I'm always up for a challenge, or for a shop to have a challenge ;) It's winter here and due to my limited garage space, doing 'internal work' is all I can do for now. Internal work will change the cost from more than 4500zl to 550zl for the parts alone.

Can anyone give me a link to a previous thread or just to highlight if what I said is correct, wrong or possible?

Thank you.

yes it's been done. you see it a lot more in the e21 community. it's not as straight forward as a regular gear swap. the case either has to be clearanced, or the carrier has to be assembled inside the case to make it work. it's not worth it unless upgrading to an ls unit at the same time.

[Polski Drywer]

yes it's been done. you see it a lot more in the e21 community. it's not as straight forward as a regular gear swap. the case either has to be clearanced, or the carrier has to be assembled inside the case to make it work. it's not worth it unless upgrading to an ls unit at the same time.

Thank you gentlemen. Essentially I'm trying to spitball between 3.00-3.46 ratio. Since the differential issue didn't occur till recently, I haven't done enough reading to exactly understand 'clearanced' and etc. Would any of you have suggestions of what diff I could try to find?

[82eye]

Thank you gentlemen. Essentially I'm trying to spitball between 3.00-3.46 ratio. Since the differential issue didn't occur till recently, I haven't done enough reading to exactly understand 'clearanced' and etc. Would any of you have suggestions of what diff I could try to find?

if you're adding power i'd go to the medium case diff and just get one in the ratio you want or swap gears in to that one. the small case might not hold up for the engine you want to swap in.

[82eye]

you might find this informative - they aren't changing cases, but it's all related

they have a few other vids on swapping cases, rebuilding ls units etc.

there is a bunch of torque values and other crucial info not included, but the assembly and disassembly process is fairly good.

[TobyB]

So for the 168mm small case differential, the lowest you can cheaply go is the E46 manual 318 ratio of 3.4x:1.

There is a 3.36 ratio that was only used in the 2002 turbo- but for that money, skip it and go to a medium case diff.

The sweet spot is to find an entire diff out of an E36ti (compact) that had a manual. They bolt in to the E30, as the rear end's the same.
For some reason, the compact (at least in the US) got a LSD pretty regularly- so you might get lucky.

The same is true of the Z3 convertible- it should bolt in. Those are a lot harder to find around here, tho.

But if you are planning to build a torquey engine, go to the 188mm diff- more useful ratios, and the thing is a lot stronger.

hth
t

[Vincenze]

If E30 differentials are not available, look for Z3 differentials. They are available in the 3.07 and 3.15 ratios that you want.

Now, it is the time when many of Z3s become partouts. Join Z3 Facebook groups in Europe and the UK to check what's available.

[Polski Drywer]

you might find this informative - they aren't changing cases, but it's all related

they have a few other vids on swapping cases, rebuilding ls units etc.

there is a bunch of torque values and other crucial info not included, but the assembly and disassembly process is fairly good.

Thank you for that useful link!

[Polski Drywer]

So for the 168mm small case differential, the lowest you can cheaply go is the E46 manual 318 ratio of 3.4x:1.

There is a 3.36 ratio that was only used in the 2002 turbo- but for that money, skip it and go to a medium case diff.

The sweet spot is to find an entire diff out of an E36ti (compact) that had a manual. They bolt in to the E30, as the rear end's the same.
For some reason, the compact (at least in the US) got a LSD pretty regularly- so you might get lucky.

The same is true of the Z3 convertible- it should bolt in. Those are a lot harder to find around here, tho.

But if you are planning to build a torquey engine, go to the 188mm diff- more useful ratios, and the thing is a lot stronger.

hth
t

Thank you and Vincenze. I have months to gather parts so what y'all said is really going to help.

Edit: Does the z3 and 318ti use the smaller differentials or the 188ish size? I'm actually having some success finding these e36 diffs, but don't know if they're made to handle for my application.

[82eye]

So for the 168mm small case differential, the lowest you can cheaply go is the E46 manual 318 ratio of 3.4x:1.

There is a 3.36 ratio that was only used in the 2002 turbo- but for that money, skip it and go to a medium case diff.

The sweet spot is to find an entire diff out of an E36ti (compact) that had a manual. They bolt in to the E30, as the rear end's the same.
For some reason, the compact (at least in the US) got a LSD pretty regularly- so you might get lucky.

The same is true of the Z3 convertible- it should bolt in. Those are a lot harder to find around here, tho.

But if you are planning to build a torquey engine, go to the 188mm diff- more useful ratios, and the thing is a lot stronger.

hth
t

the ti is a direct bolt. the axles have to be modified on the z3 for an e30.

[82eye]

Thank you for that useful link!

if you get far enough i have some torque values. they are not always easy to find. i've worked on bmw and a few other diffs.

[Vincenze]

Edit: Does the z3 and 318ti use the smaller differentials or the 188ish size? I'm actually having some success finding these e36 diffs, but don't know if they're made to handle for my application.

You should be careful. Different Z3 models had different differentials.

I guess the 4-cylinder Z3s had the weakest ones.
The 6-cylinder Z3s had nice Torsen differentials.

If you look at this 3.07 Z3 differential, it has a very sturdy rubber bushing, but the output side flanges have a different bolt pattern - they can easily be exchanged to E30 flanges.

https://www.ebay.com/itm/373689203112

There are 3.25 Z3 differentials, but they cost much more.

[Polski Drywer]

You should be careful. Different Z3 models had different differentials.

I guess the 4-cylinder Z3s had the weakest ones.
The 6-cylinder Z3s had nice Torsen differentials.

Thanks for posting the ebay link but I'm still getting a bit confused with at least the 318ti and z3. I do want to go with an engine that has more power and more torque. Beyond the 6 cylinder engine z3 differentials, am I wasting my time with the 318ti (compact) differential? I see advertisements for "e36 dyfer Duza Glowa" which means something like 'e36 big case' and then I'm finding "e36 compakt" which I assume is 318ti small ones.


For example:

This one is duza glowa and compact. This is one of the ones I should be looking for?

vs.

Stuff like this or this

I really appreciate the help but my poor grasp on Polish is interfering with all of your guys' help. Thank you!

[TobyB]

Does the z3 and 318ti use the smaller differentials or the 188ish size?

The 318ti will always have the smaller 168 diff. The 6 cylinder version (323 kompact?- they didn't make many) got the 188.

Likewise, if the Z3 had the 1.9l 4 cylinder, it'll have the smaller 168. If it's got the 6, it SHOULD have a 188. The POSSIBLE
'gotcha' here is that the 2.0L 6, that we never got in the states, MIGHT have a smaller diff in the earlier cars.
www.realoem.com is USUALLY right about this stuff, and helps with ratios.
As to limited slip, it's going to vary by year, engine, package and market.

It sounds to me like you ought to go looking for a 6 cylinder Z3 188. As far as I know, the case will always work,
but the output stub shafts will be different- you'll need stub shafts- output flanges- from a 188 E30 diff.

Hmm. I looked at your links, and I might be wrong about ratios- that 3.38 looks like a small case.

I went out and took a picture under the 318ti- the small case diff has one bolt on top and bottom,
whereas the medium 188 has 2 on top and bottom.

hope this helps,
t

https://www.saabnet.com/tsn/members/gallery.html?memberID=2653&do=show&id=55338

https://www.saabnet.com/tsn/members/gallery.html?memberID=2653&do=show&id=55339