How do I drop a M42 into a e30 325i?

[rwinter]

Hi

I'm transforming my '84/'89 325i into a 318is. Not sure what all is different on the cars. I'm hoping the front crossmember is the same. Not sure if the diff is the same or not, and what driveshaft to use. Can anyone lend some help here? As far as the tranny, curious what ratios are available. Can you bolt on a Z3 transmission? I have heard that the z3 has a nice close ratio tranny.

[Febi Guibo]

kidneyboy has done it... maybe send him a PM if he doesn't pick up this thread.

The M42 uses a getrag 240 transmission... I'm not sure what model the Z3 1.9 transmission is, but you might be right...

I poked around and the ratios are something like this:

getrag 240

1st: 3.71
2nd: 2.02
3rd: 1.32
4th: 1.00
5th: 0.81


getrag 245 close ratio/"dogleg"

1st: 3.764
2nd: 2.325
3rd:1.612
4th: 1.229
5th: 1.000


Z3 1.9 tranny:

1st: 4.23:1
2nd: 2.53:1
3rd: 1.66:1
4th: 1.22:1
5th: 1.00:1

[StreetSpec_iS]

feck me, it does have different ratios. nice find.

[sheepdog]

The trannies do not interchange, different pattern on the bellhousing at least (I think).

Keep in mind the 318's weighed about 200 pounds less and it was not all engine.

[asubimmer]

engine, tranny, diff, no trunk tar, ...


just some of the reason's the 318's are lighter

[jbuttenshaw]

i turned my 83 318i into an is so i did virtually the same thing, crossmemebers are the same, may need some slight filing but i did it, diff in is is 4.1 but u can use a different one as long as its not too low, tailshaft out of my m10 worked with the m42 so maybe they were all the same, either way can;t be too hard to get one, i hear the e36 m42 harmonic balancer doesn;t thave the 7200rpm problem so that could be insentive to get that, i got the e36 one but mainly coz its newer and has knock sensors which i thought might some in handy for turbo if i wanted too, harmonic balancer thoery is hear say only so take with grain of salt, however, the e36 318is with the m42 has a close ratio gearbox, same first five ratios of that of the e36 m3, and if ur diff is 3.25 which i belive it is or close to i'd go that engine combo with ur diff, needs some driveshaft and shift linkage mods but would make a nice setup. hope that helped.

[rwinter]

Thanks for the input guys. Darn it I would love to have those better tranny ratios but my racing class won't let me go to a tranny with a 5 speed where 5th is 1:1. Were the 318is diffs limited slip and all 4.1:1? Will the e36 diff fit in my e30?

Thanks again!

[Febi Guibo]

Limited slip was an option... I think the all the cars had 4.10 ratios in the rear end.

A larger diff will fit, with some modfications...

if I could handle the custom work required, I would consider going to a getrag 260 and a 3.46 medium case diff (similar to a z3 1.9)

...it's a little quicker through 1st and 2nd, and it nets out to be about the same in 5th as a getrag 240 with a 4.10. Plus, as noted above, 5th is a straight 1:1 from the flywheel.

Most models of the getrag 260 are better built (there are some variations) and a medium case diff would last forever on our cars. The bigger diff is like an extra 16# in the rear tho.

[2002maniac]

Thanks for the input guys. Darn it I would love to have those better tranny ratios but my racing class won't let me go to a tranny with a 5 speed where 5th is 1:1. Were the 318is diffs limited slip and all 4.1:1? Will the e36 diff fit in my e30?

Thanks again!

All 318i's and is' came with a 4.1:1 rear end. LSD was optional. The M42 318ic has a 4.27:1 rear end but finding one with LSD is rare.

The only e36 diff that will swap into an e30 is the one in the 318ti hatchback.

A larger diff will fit, with some modfications...

Nope. No modifications necessary to fit a medium case diff from a e30,e28, or e24. The diff's mount exactly the same and the flange width is also the same. If you get a diff from a e28 5-series or e24 6-er you will need the rear cover from a e30 medium case diff.