1990 318i m42 engine swap

[Gapin it]

Hey there, new to this forum. Just picked myself up a 1990 BMW 318i with an m40B18 and as some of you probably know, not exactly the fastest car around. I was originally planning on rebuilding the engine with worked cams, high comp pistons, chipped ecu etc. But am wondering if its worth swapping in an m42b18 ? how hard is it to swap an m42 into a 318i? ive read that its not worth modding the m40 and it'd be better to do an engine swap for the money. What are your thoughts? Apparently my m40b18 transmission should bolt up to an m42 and its pretty straight forward doing the swap.

What about wiring?

Thanks in advance.

[Gapin it]

Or maybe even an m20b25 or something similar? I just want something that can spin the wheels, doesn't cost the world on petrol. And can accelerate nicely with a bit of torque to push you back in the seat and for boosting out of corners and things. I'd like it to have the least amount of work possible aswell. So don't think something like an m50 is for me as i'd like an engine that just drops in and has a decent amount of power and torque gain.

[DesktopDave]

How many of the easy mods have you done?  Lightweight flywheel, fan delete, synthetic oils, etc?  Those will all help a bit.  Seems like you're running larger wheels...what's your diff ratio?  You might have too much tire for the motor.

The M20 and M52 are about the same amount of work.  They both need a new transmission, clutch & likely a diff.  The newer motor will be easier to find in good condition, but I'd suspect a bit more money, especially in running costs.  They also make the car a bit more nose-heavy.

The M42 is a lot better choice if you'd like to keep the car's  handling.  It also give you a bit more power, similar economy and  longevity.  Mine's run almost 300k miles.

From what you're saying I'd suggest a turbo setup.  It'll keep the nice balance of the M40 but give quite a bit more power.  It's not cheap to do it right, but it'll give the best performance all-around.

[Gapin it]

I would love a turbo setup but i would need a few custom mods. Do you know how easy it is to swap an m42 into a 318i? Could i use the same transmission. Also im sure my differential is a 4.10

[DesktopDave]

I'm pretty sure they all use the Getrag 240.  Same input shaft size, clutch, fork, etc.  The 4-cyl blocks are very similar (if not nearly identical from what I've been told), M40/M41/M42/M43/M44.  Some cams are belt driven, like the M40; some are chain driven, like the M42.  I'd assume that the timing cases are different.  Kinda makes me wonder if you could just swap the head & manifolds?

There might be a few harness differences but I think all late e30s are very similar.  Double check the C101 pinout (large body harness connector on the firewall).  If you find a good M42, I'd be sure to grab the wiring harness as well.  I'd be tempted to keep a transmission attached to it as well.  SHOULD all be plug-n-play.

The only trouble I can see is if you get a later M42 (>1994 IIRC), some of the ECU/DME's are encoded with EWS to protect them.  They'll only work if they have the security system intact.

[Gapin it]

Great thanks, Yeah i read that the m40 and m42 have the same block. So it should be alright, if i can get a transmission for a good price i will be sure to get it but for the moment my current one is fine. Do you think an m42 out of an e36 will have a different wiring harness than one out of an e30?

[DesktopDave]

Take a look through RealOEM to be sure.  My answers are all to be taken with a grain of salt...but it depends on the year.  The early e36 motor looks very similar.  Then BMW added the dual-resonance manifold (DISA), knock sensors and then EWS.  You can mix and match the later motor with the earlier manifold, and the sensors should all be the same.  The e30 M42 harness has been used to run the later e36 motor.  I'm not sure about the M40 harness as we never had them here, but I'd expect they're very similar.  I'm told that the later DISA manifold will not clear the hood of the e30.

It's a popular mod here to swap the chain cases off late M42/M44.  The later M44 is a better design...it eliminated the deflection gear, updated the chain guides and tensioner.  Highly recommended upgrades.

[Gapin it]

Alright great thanks, Im interested in doing an m42 swap with lightened flywheel etc basic things and then eventually turboing it. Ill have a look around my local yards to see if i can find an engine, thanks. Do you have any more information on m42 engine swaps?

[DesktopDave]

I did find this, has some good info but it's not perfect:
http://www.m42club.com/forums/showthread.php?t=4414

Seems like the big parts are easy, the wiring gives trouble.  Be aware that any e36 motor will require an e30 oil pan.  The e30 oil sump & pickup are to the front.  The e36 has a more protected setup to the rear.  It won't drop right in.  There are also several versions of belt drive.  Later M42's have serpentine-style belts instead of vee-belts to drive accessories.  You'd pretty much have to grab the whole front end of an M42 for it to work.

IMHO that's a lot of time, money & frustration for 30hp.  As much as I like the M42, it still only ~144hp vs. ~115hp of the M40B18.  Even a well tuned M42 only does about 160hp.  An M52B28 swap would get you over ~220hp, and it's very well documented.  Of course it'd be a lot more fuelish and the extra weight up front will dampen the delightful handling of the M4x.  Much more bang for your buck, different compromise.

Turbos are a pretty cheap solution to your question too.  I'm no expert, but they seem to go under $3k for a really great setup, and you can pretty much dial your power/cost ratio.  I'd bet scrounging some decent parts from the ricer crowd along with a Megasquirt/VEMS/WBO2 could keep your cost well under $3k...and give you a reliable 50% increase without any need for the 16v head.  You're luckier in that sense...the M40 has a much narrower head than the M42, allowing more mounting choices for the exhaust manifold.

[Gapin it]

So you think i should just scrap the idea of swapping in an m42 and turboing it, and instead, just turboing the m40? 180hp would be enough for my needs.

[DesktopDave]

Just seems that way to me.  Don't get me wrong, I love the M42.  The more of them the better.  But I'm essentially a cheapskate.  If I want to increase performance I've done it with weight removal, aerodynamic tweaks, and suspension/brake upgrades.  I'm in the midst of getting the most out of my motor...with the best synthetic lubricants, effective cooling, cutting parasitic drag, tweaking fuel injectors.   I'm currently contemplating a WBO2 unit to be sure the car is running at its best.

Wait for a few of our tuners to chime in.  They've done amazing things with alternative cranks, superchargers & turbos.  Cost and complexity are all over the map, I'm sure.

Before I buy anything I just add up the baseline numbers first.  Paper is oh-so-much cheaper than parts!  It's easier to dig through EBay or CL for what I'd like.   It always seems that it's the little bits that make the most trouble, so I'm sure to do a lot of research first.

Speaking of deals, I nearly pulled the trigger on a nearly-completed e30 S52...the owner had a change of heart (tired of chasing wiring troubles I'd figure) and prepared to sacrifice the whole project for ~$3k.  Very tempting, considering the Euro M3 motor!  Those run about 330hp...not much like my little M42 but no doubt a load of fun.

[Gapin it]

That would be awesome. All that power in such a small car. Im still thinking about m42 swap aye but the only problem i can think of is wiring. Turboing the m40 would be cool but i would need custom mani etc and apparantly m40s timing belts fail with some more power.

[Gapin it]

anyone got any information on turboing the m40?