Author Topic: M42 to M20 Swap (Read 9992 times)

HHH_SSS · « **on:** March 27, 2010, 02:48:04 PM »

I have a 1991 318IS, I love the car, but the power does disappoint me a bit. Im looking for something with more power. I dont have the kind of money to try and go the forced induction route so I have been thinking about swapping in a 6 cylinder. i know there are some beefier engines I can swap in, but I found a great deal on an M20B25 from a 1990 325ic with only 109k on the motor. I was wondering if any of you could tell me what is everything i would need to do a swap? ECU, Wiring harness, driveshaft, etc.

1991 E30 M42 · « **Reply #1 on:** March 27, 2010, 05:42:47 PM »

you may want to check r3v as this is m42club and we love out m42's

HHH_SSS · « **Reply #2 on:** March 27, 2010, 06:36:46 PM »

Haha I see what your saying man. Don't ge me wrong I love my m42 more than any car i've had. I just want more power out of it, i want to go turbo with it, but it seems like its a bit complicated and pricey.

DesktopDave · « **Reply #3 on:** March 27, 2010, 06:41:01 PM »

You'd need the motor, tranny, drive shaft, likely the diff, the engine wiring harness, DME, air box too. Radiator, expansion tank, all coolant hoses. I'm not 100% sure that the compressor is the same unit either. Engine mounts too. Might need a tranny subframe. Front springs are different because of the longer engine.

I'd take the whole front clip for something like this. You know that the M20 has less than 40 hp than the M42, right? You could get a COP kit, MarkD chip and a nice open element filter to make that up. You'd be out what, $500? Less than the M20, I'll bet. And a bit easier to install.

1991 E30 M42 · « **Reply #4 on:** March 28, 2010, 01:39:46 AM »

Quote from: DesktopDave;90122

You'd need the motor, tranny, drive shaft, likely the diff, the engine wiring harness, DME, air box too. Radiator, expansion tank, all coolant hoses. I'm not 100% sure that the compressor is the same unit either. Engine mounts too. Might need a tranny subframe. Front springs are different because of the longer engine.

I'd take the whole front clip for something like this. You know that the M20 has less than 40 hp than the M42, right? You could get a COP kit, MarkD chip and a nice open element filter to make that up. You'd be out what, $500? Less than the M20, I'll bet. And a bit easier to install.

+1
a set of cams from delta as well

Fraser · « **Reply #5 on:** April 14, 2010, 08:47:30 PM »

It's not quite THAT complicated, but still not really worth the work when you're not gaining a lot. m50 would make a lot more sense.

I have an m42 and an m20iX car. I swear the 318 is faster sometimes, and a lot more fun to drive. (granted a 4x4 6 cyl e30 is a ton heavier than 2wd 4 cyl car.) I do know the 318 gets about another 10mpg also.

Romrog318is · « **Reply #6 on:** April 14, 2010, 09:04:54 PM »

why would you spend the money on that swap for only 19 HP? get a mark D chip and a 373
when i had my M42 in my car i could smoke stock 325i's and some chipped ones...

now its basically to easy

Romrog318is · « **Reply #7 on:** April 14, 2010, 09:08:46 PM »

M42 144 stock
M20 170 so its acctually only 26 HP

BlueBMW · « **Reply #8 on:** April 14, 2010, 09:14:15 PM »

Driven properly, the li'l M42 can keep up with the best of em! And the M20 has all that extra maintenance.... rocker arms breaking, timing belts, distributor caps.... the M42 is so much simpler IMO.

Romrog318is · « **Reply #9 on:** April 14, 2010, 09:47:26 PM »

^^ what he said!

and i wish my motor was this simple! haha

polkadot_boxerman · « **Reply #10 on:** April 15, 2010, 03:36:01 AM »

what kind of power gains are we talking about when just throwing in a 373?

Fraser · « **Reply #11 on:** April 15, 2010, 08:57:41 AM »

Quote from: polkadot_boxerman;90912

what kind of power gains are we talking about when just throwing in a 373?

None.

And, the m20 is actually a ton simpler. Other than the t-belts and occasional rocker arms they're pretty much bulletproof. No loose oil pan nuts, weird timing gear, profile gaskets, vacuum hose nightmares, etc... My m20 has 277k on it and doesn't skip a beat.

That having been said, I still enjoy driving my m42 car a bunch more than my m20 car, and the work I've had to do to it is pretty minimal.

Romrog318is · « **Reply #12 on:** April 15, 2010, 05:26:28 PM »

Quote from: polkadot_boxerman;90912

what kind of power gains are we talking about when just throwing in a 373?

none but my M42 with the GR 240 from an E36 could get 70 in 2nd with it

DesktopDave · « **Reply #13 on:** April 15, 2010, 06:32:40 PM »

I'd say the 3.73 helps a stock M42 stay in its power band. I did it to mine and it really makes for a far smoother car particularly on the highways. I still start in 2nd a lot of the time, at least when Pittsburgh's pretty steep hills allow.

The 3.73 would be ideal for a chipped M42, especially because it's rated for much more torque. The stock 4.10 is too high a ratio and too small to last IMHO. On the downside, a medium case diff is about 20 pounds heavier.

deekay · « **Reply #14 on:** April 19, 2010, 01:28:51 AM »

you'd have to be kinda retarded to do this swap IMO.

starting with an m42 car makes an M5X/S5X swap easier... why would you do more work to put in an older, less reliable engine that makes less power?