ZF S5D 310Z trans & M20 engine

[germancarsonly]

I posted this in the transmission section, but I don't think many people go there unless they need help themselves. So to get noticed I'll start it here:
I am going to stick a ZF S5D 310Z behind my M20 engine. Can anyone offer any tips or advise? Has anyone done this?

[germancarsonly]

I posted this same question at BayE30 and got this reply this morning:
You'll need a modified transmission bracket (probably the hardest part). Jason will also give you the good advice of matching your starter to your flywheel... Probably also some custom shifter hardware. Never measured the length of the two, but it might also upset the driveshaft length.

May I ask why? The e30 Getrags have been known to take tons of power.

My reply:
I am thinking that I am going to have to modify the rear trans bracket and do the opposite of what the guys running the Getrag 260 behind the M50 engines are doing. That part is simple as I can do my own fab work and have a nice welder. I want to run the early Euro M20 flywheel and I will just use the original starter. The starter only cares about which flywheel it needs to play with and it doesn't interact with the trans anyway. The shift console length might be OK using the E30 parts, but I need to measure the distance between the ZF and the old Getrag and I haven't done that yet. I know I need to bring the shift lever back to the center of the hole in the tunnel and that should be very easy to do. Again, I'm thinking I just need to do everything backward from what the M50 + Getrag 260 folks have done. That should be the simple stuff.

My drive line has the small Guibo and the trans has the big one. I think the guys running this tran behind the M50 engines just use the 1986 shaft that had the larger one and then use the correct center bearing for their year car. This sucks a little as I have a rebuilt drive shaft with replacable U-Joints, but I will have to find another shaft now.

I plan on sticking an M20 short block with trans attached on a bench this week and mocking up anything I need to do. I'll look at it first with the Getrag and then hang the ZF on it. I think my biggest concern is the throw out bearing movement. The M50 flywheel that this trans was mated to is pretty thick. I wish I had measured the distance from the back of the M50 block to the rear of the presure plate when I removed the trans, but I didn't do it. I may be able to measure one this week and that will tell me more. At least by doing it up on a bench it will be easier than trying to figure it out under the car.

I know the Getrag is a pretty bullet-proof transmission and probably stronger than the ZF, but the gear ratios are wrong. I've been in a couple of E30 cars now with the ZF and the closer ratos in the trans are just plain nicer. I also have an 1993 E34 with a manual trans that I drive most everyday and I like it. You know most of the earlier Euro M20 powered cars had the close ratio Getrag. Then they built a bizillion 2.7 eta powered cars and the overdrive trans seemed to be a good match for that purpose. But, when the 2.5i cars came out they continued to use the overdrive trans???

I'm sure I am missing something. What?

[SpecM]

just use a shorter diff (like a 4.10)... same effect as a close-ratio trans.

but it looks like you have some fabbing to do. Pretty much the opposite of what the m50/g260 guys go, like you said

[germancarsonly]

Well, I already have a 4.10 LSD and I do like the low rear end ratio. I want the trans gears spaced closer and the ZF will do it.

I was gone all day today on a "spirited" drive up in the Sierra foothills in my E34. It has the later Getrag trans, but the ratios are the same as the ZF. My M20 engine makes more HP and Torque than the M50 in my E34 and the E30 is lighter. During the drive today I think I figured out most of what I need to do and will get on it this week. Still if anyone has any input or if they are interested in doing this swap - chime in. I will build a jig for the trans mount when I modify mine so I can make clones and the same for the shifter mod.

[SpecM]

you're insane

[germancarsonly]

You aren't the first person that has told me that. Thanks anyway.

[SpecM]

Thanks anyway.

you're welcome

I don't see any big issues with the install that you havn't adressed
you'll have to use a different driveshaft, search in the 24v section for what the s52/zf310 guys use

[euroshark]

If your M20 makes more power and torque than your M50, and you already have a 4.10 diff, what reason would there be for closer gear ratios? Why not drive in such a way that you use the torque that is available or spend money and time on other mods? I have a 6 series with a close ratio box and it almost seems like a waste with so much torque available... Not to mention the top speed is gearing limited to about 130mph (maybe a little higher with my 6800rpm red line - not that I'll ever use it) and that's with a 3.07LSD! I could see a point in doing what you are talking about on a race car or auto-x car, but on a street car?? I'm not making fun, just curious.

[germancarsonly]

I want to take my car to the drag strip regularly when it's back together and the closer ratio gears are going to be good for that. The car isn't going to be street driven very much. I don't really care about the top end speed of this car and have a couple of other BMWs with enough top end if I need that.

I guess I need to move this over to the transmission section now. I have an idea that what I want to do hasn't been done by anyone yet.