Fitting m20 into m42 e30 318is help

Post Fri May 16, 2014 10:14 pm

Hey guys on the forum a gud few years but have never really posted much as I sold my old e30 318is.
But in the last year I bought another 1 a 1990 318is and today I bought a crashed e30 325i sport off a mate going doing the swap this week. I'm gonna fit engine box prop shaft rad etc.
But am a bit confused about the wiring as there's a lot of conflicting info on the swap. s this brings me to my questions:
1. Is the loom a straight plug and play?
2. I have a medium case 4:1 on my own car and there's a 3.91 on the donor just wanna no what people are running and how they find them?
Thanks in advance for any help nd I'm gonna try get a build thread up on this

Post Fri May 16, 2014 10:16 pm

http://www.e30zone.net/e30zonewiki/inde ... Swap_-_M20

The normal diff for a 325i is either 3.64:1 or 3.91:1 (Sport LSD). Seeing as you have the 3.91 LSD, you may as well fit that, as a small-case diff won't like the torque of the M20B25.

Post Fri May 16, 2014 10:33 pm

conormc85 wrote: 1. Is the loom a straight plug and play?

Check that pin 20 on the car side of the C101 engine loom plug/socket doesn't have a plain brown wire connected to it. If it does, cut it away and insulate the end of the wire.
If the iS has ABS brakes, you may need to add a wire to pin 20 of the M20 engine loom.

Post Fri May 16, 2014 11:46 pm

@ speedtouch ya I've read the e30 swap wiki good guide just not too sure on the wiring side model specific
The 4:1 is medium case lsd just wondering about pros and cons of each diff thanks for the quick reply

@brianmooore cheers man is that the only wiring change u no of have u done this swap before I've no abs on the IS
Wondering aswell about d relay position on the IS its on the bulkhead and on the 325 it's on the inner passenger valance thanks for the quick reply aswell.

Post Fri May 16, 2014 11:56 pm

A 4.1:1 diff will be rather too low-geared for an M20B25 - not good for motorway cruising.

But, it would give lively acceleration!

Post Sat May 17, 2014 12:57 am

I must put new clutch plates in my 4.1 any way so might leave it in for a couple of days after the swap just to see how she copes with the m20 and put in the 3.91 while I do the other 1 just so I can compare and choose thanks again for the input. My mate reckons the ecu in the 325 was chipped but won't really know till I get it out I only got 1 spin in it as he only had it a few weeks when he put it in a lamp post if it's not I might get onto you about a chip it's a standard m20 is there much gains to be had from 1?

Post Sat May 17, 2014 11:21 am

You can usually tell if it's been chipped just by looking at the ECU lid tabs - if they appear to have been bent up, then it's probably been chipped.

An original BMW chip will have a silver label on with a part number, e.g. 1 267 356 378.

A chip will give typical gains of 8-12bhp, smoother driveability (irons out flat spots inherent in the standard program) and a raised rev limit. You can expect to see 2-3mpg gain in fuel economy when driven gently. So yes, worthwhile gains to be had, even on a standard engine.