M20 engine swap into 320i

[todor]

I know this topic has been discussed a gazillion times, but I'd like to compile all knowledge into one thread so that other people (and I) can refer to one centralized place about the M20 conversion. I have many questions on the subject, which I've written in bold red text. If I've given any wrong info, please correct me. Thanks.

The engine:
I've decided to go with a M20B25 from a '87-'91 325i/ic/ix or '89-'91 525i. This 2.5L SOHC I6 engine makes 168hp and 164lbft of torque and uses a Bosch Motronic ECU. Ignition: 1 coil and a mechanical distributor, exact spark timing controlled by the ECU. Fuel: individual injectors for each cylinder (mounted on intake manifold), also controlled by the ECU. It has an O2 sensor before the catalytic converter.
It's also possible to transplant any other M20 engine into the 320i, but the M20B25 is the newest of the series and has the highest amount of power in its stock form. The 2.7L SuperETA engine from a '88 325 (not "i") or '88 528e supposedly also has a lot of potential (it uses the "i" head minus the camshaft).
Why not the more modern M50/S50/M52/S52 engines? Well, that's certainly an option since those engines require the same physical mounts as the M20, but they are more complex engines and would require more work to hook up the electronics and make everything work, plus they mount to the transmission at a weird (rotated) angle. It's a path much less explored than the M20 swap. Plus they are heavier... And there may actually be such a thing as too much power for an E21 - the one case of an M50 swap that I know of had cracked structural parts due to the high torque of the engine.

Other parts needed for the swap:

• Everything that's attached to the M20 engine, including:
  • Wiring harness and Motronic ECU, along w/ the 3 engine relays (main, fuel pump, O2 sensor) that are attached to the wiring harness
  • Intake manifold, MAF, sensors, ICV, all vacuum hoses
  • Exhaust manifold (an aftermarket header or a E21 323i exhaust manifold will work too)
  • All fuel injection and ignition parts
  • Starter
  • Alternator
  • (I personally will get rid of the A/C and power steering pump. Each is on a separate belt, so removing them doesn't interfere with the alternator or water pump)
• Front subframe/crossmember from a 6-cyl E21 (nothing else fits without major modification)
• Engine mount brackets (metal) and rubber mounts from a 6-cyl E21 (the rubber mounts from a E30 6-cyl may fit, possibly with some modification)
• Transmission from a 6-cyl E21 (or from a E30/E28, but see this link) along with the transmission crossmember from that transmission (an E30 one would need to have the holes redrilled, but works fine for an E30 tranny)
• Shifter linkage from whatever transmission you use. This includes shift plate/support, shift lever, shift selector rod, and selector-rod-to-tranny coupling. Note that the E21 323i selector rod has larger-diameter than the US 320i one and the E30 one, so the components can't be mixed.
• Flywheel, clutch, pressure plate, etc. from any M20 engine (E21 323i flywheel is preferable because it's lighter, but any will work). Just don't mix-and-match clutch components from different engines.
• Clutch slave cylinder from the E30 325i (works with E21 or E30 tranny). The E21 4-cyl slave cylinder may work too, but I haven't tried it (but they looked the same visually)
• Driveshaft: get the stock 320i driveshaft professionally shortened to fit or, if using an E21 6-cyl transmission, you can get the stock driveshaft from that same model (note that 4-speed trannies have a 4-bolt flange, whereas 5-sp ones have a 3-bolt flange, so a matching driveshaft is required... or you can swap flanges I guess). The flex disc/guibo is the same part number for all 3-bolt-flange E21s and E30s. Note that an E30 driveshaft does not fit for many reasons, including length and position of center bearing.
• Exhaust downpipe from E30 325i with re-welded O2 sensor bung (original position puts the O2 sensor in a place where it hits the frame rail, so it needs to be relocated)... or get an aftermarket header for better performance.
• A custom-made exhaust to fit whatever downpipe/header you're using; a complete Euro E21 320/6 exhaust may fit with some modification, including a custom O2 sensor bung. (The 323i dual exhaust does NOT fit without very major modification to sheet metal)
• Radiator, radiator hoses & expansion tank from a 6-cyl E21. Bottom radiator mounts (rubber circular mounts) from any 6-cyl E30 or E21. Top radiator mount from 6-cyl E21. Expansion tank from an early-style E30 will also fit; late-style E30 expansion tank mounts to the other side, but if you figure out where and how to mount it, that might work too.
  
• Water pump from a 2.7L (ETA) M20 engine, so that you can hook up the expansion tank to it. Other setups are also possible, but this one is the easiest.
• Keep the belt-driven fan from the M20B25 engine if you have a 1980+ E21. It fits fine with the 323i radiator in front of it. However, I've heard that '79 and older cars have less room, so you may need to use an aftermarket electric fan instead.
• Throttle cable from a E30 325i (modified somehow to hook up to the E21 pedal), or the stock E21 throttle cable modified somehow to hook up to the E30 engine (I did the latter with modification to the E30 throttle body levers).
• Air intake routing/filter is easily replaced with a cold-air intake (cone filter, etc.). A stock E30 air box should also work with some custom brackets if you insist. In either case though, use the stock E30 air flow meter.
• Oil cooler from E30 325i (it's also possible to bypass the cooler using a bracket from an E30 325e, but it's always better to have more cooling.
• Fuel system: use the external fuel pump from an early-style E30 (up to 87). Remove the E21 fuel accumulator because it interferes with the function of the E30 fuel pressure regulator, which is on the fuel rail on the engine. Custom hose hookups are required for this. I also used an E30 fuel filter because it's difficult to get the right hoses with banjo fittings for the stock E21 fuel filter.
• Tachometer from a 6-cyl E21 (do other 6-cyl-Bimmer tachs work? which ones?)
• Cables, brackets, etc. to relocate the battery to the trunk (for more space in the engine compartment, plus better front-to-back weight distribution). I used the stock battery cable from an E30 along with the stock E30 battery terminal in the engine compartment. However, the cable is a bit too short, so for anything other than a track car (i.e. if you need to route it well out of sight) a longer cable will be needed.

Procedure (under construction... it'll be more detailed in the future):

1. Disconnect everything from old engine, remove old engine
2. Relocate battery to the trunk, cut out leftover battery tray and air intake brackets
3. Replace front crossmember w/ 323i part
4. Install new engine & transmission (either as 1 unit or separately)
5. Put in new radiator (cut out front radiator support and tuck in the radiator into the front end of the car), hook up coolant hoses
6. Install new fuel pump or FPR and hook up fuel lines
7. Hook up throttle cable
8. Hook up electrical connections (see Motronic wiring link below)
9. Have driveshaft shortened and attach it
10. Go for a drive

Links:
I got most of the info here:
Swap info (M20B25 into Euro 323i): http://www.e21bmw.net/graymarket/library/swap.php
Swap info (M20 into US 320i): http://www.e21bmw.net/graymarket/library/swap2.php
E30 Motronic vs. E21 323i wiring diagram: http://www.e21bmw.net/tech/motronic.php
... and on various forums, mostly here on bf.c


So! The idea is that the red text will disappear little by little as my questions get answered and I fill in the missing info. Thanks in advance.

[Need4Speed1299]

I hate to thread jack you, but ive always wondered.. Can you use an E30 subframe?

[Banned318ti]

Originally Posted by Need4Speed1299

I hate to thread jack you, but ive always wondered.. Can you use an E30 subframe?

Thats a nice question for The OP! he should take that into consideration

[todor]

Originally Posted by Need4Speed1299

I hate to thread jack you, but ive always wondered.. Can you use an E30 subframe?

My guess is 'no' because otherwise i would have heard about it, but i've added that question to the original post.

[smstevenms]

Wouldn't it be easier to swap with something that you could take everything from to transplant? That's what I'm hoping for on my project.

[todor]

Originally Posted by smstevenms

Wouldn't it be easier to swap with something that you could take everything from to transplant? That's what I'm hoping for on my project.

it would certainly be easier, but as far as I know, no such model exists - that you could take everything out of and just bolt it into the 320i.

[Rickysbmw320i]

here you go, this guy is from here on the forums, mabye he will ship it to you. no, you cant use the e30 subframe. http://sfbay.craigslist.org/nby/pts/444485454.html


Rick

[Scott72]

I'm in the process replacing my 2.7 eta motor (with a four barrel carb from the original 2.0 m20) with a 1990 M20B25. Maybe I can answer some of your questions as I know it.
I'm running headers, but I had a "bung" welded in for the oxygen sensor. If you run 320/6 or 323i exhaust, you'll want this done. Doubt you could run E30 exhaust without a lot of chopping and fabrication. Don't really know about the exhaust manifolds, but I think they are different. I can check - I have both at home. I will have a complete custom exhaust (duals with Cat) that i will be pulling off to replace with the stk exhaust (323i) except the headers if someone wants it. It's a little loud for me.
You'll probably want an ETA water pump, it's the easier route. Guys have used E30 radiators with the M20B25 pump setup, but I think there is some cutting involved. May be different in a US car. I run a 323I radiator now with a ETA pump and have no issues, although my car is a grey market.
If don't want to fabricate, find a E21 323i or 320/6 subframe. The E30 is different. This way everything will just bolt up. A E30 subframe is not going to bolt up.
The stock air box will fit in an E21 (although some brackets may need to be fabricated to mount it). Not sure were the battery is on a US 320I, but in a grey market car it's on the drivers side in back of the headlight bucket. To fit an e30 box the battery tray must be cut out and the battery moved to the trunk. That has been done in my car already. Not a difficult process and helps offest the weight of the M20. Then you have the room to fit the e30 airbox.
Your gonna want to use the M20B25 MAF unless your running something more exotic.
There is not reason not to run the e30 oil cooler. Pretty easy to mount behind the front valance. You can run without it too if you want. My ETA motor now doesn't have an oil cooler. I heard you won't have a overheat issue without it running a M20B25, but it can't hurt in my opinion.

Hope this helps a little

[todor]

That's great info Scott72! I've updated the original post to incorporate it.

[smstevenms]

todor, I don't literally mean bolt right in. I mean with modification.

[todor]

Bump... people, please answer my questions in the original post.. thanks.

[todor]

Originally Posted by smstevenms

todor, I don't literally mean bolt right in. I mean with modification.

Yeah, I understand you. Well I guess the S14 that you've got your eyes set on is probably an easier swap, but I have no idea. Hopefully people will answer your questions in your other thread.
This thread is supposed to be about the M20 swap and the reason why I chose M20 is that it's been done many times already, so people can provide info, and also that it seems to be the cheapest engine to swap into an E21 (even after you include all the additional parts that are necessary, as listed in my original post). It also helps that the E21 was offered with a M20 from the factory, so a lot of stock 323i parts can be used for this project.

[smstevenms]

I hear you, sorry bro. It's seeming more & more I'm not going to be getting this engine. This isn't responding to my phone msg., not picking up phone. He me an email yeterday to call him today and gave me another email to contact him and nothing. So fustrating, all want to do is ask the guy some questions before I commit to anything. GRRrrrr.

[Need4Speed1299]

Lets keep this thread alive. It will cover a ton of FAQ's.

[smstevenms]

I did get a hold of the guy, and it's a deal. But I have to go pick it up.

[todor]

Yes, let's keep this thread going and let's keep it on topic - the M20 conversion (not the S14 conversion or any other topic).

Can't anyone answer my questions in the original post?

The most important one is does a driveshaft from a 6-cyl E21 bolt onto the 320i/is diff with no modification? This is assuming I'll be using a tranny from a 6-cyl E21 too. Is there any difference between the 5-speed tranny from a 323i and the one from a 320/6? What about the driveshaft?

[todor]

Bump... I still have MANY unanswered questions. Help please.

[hdx]

Originally Posted by todor

Yes, let's keep this thread going and let's keep it on topic - the M20 conversion (not the S14 conversion or any other topic).

Can't anyone answer my questions in the original post?

The most important one is does a driveshaft from a 6-cyl E21 bolt onto the 320i/is diff with no modification? This is assuming I'll be using a tranny from a 6-cyl E21 too. Is there any difference between the 5-speed tranny from a 323i and the one from a 320/6? What about the driveshaft?

Yes it does I have two e21 323i trans 1 4 speed & 1 5 speed . The 4 speed is a 4 bolt output shaft and the 5 speed is a three bolt output shaft. The 5 speed e 21 drive shaft from a 4 cyl car is the same size as a 4 speed 6cyl car , but with 3 bolts , if you make it 3.1" shorter it will work for a 5 speed 6 cyl e21 trans. I shortend mine by marking it cuting out the 3.1" , then I made a sleve out of some 4130 from aircraft spruce , milled it a little for a nice tight fit lined it up and tig welded it, works nice. the e21 also has sloted holes in the rear sub frame this gives you a little room for error. 323i and 320 6 same size on the trans and drive shaft.

[todor]

Originally Posted by hdx

Yes it does I have two e21 323i trans 1 4 speed & 1 5 speed . The 4 speed is a 4 bolt output shaft and the 5 speed is a three bolt output shaft. The 5 speed e 21 drive shaft from a 4 cyl car is the same size as a 4 speed 6cyl car , but with 3 bolts , if you make it 3.1" shorter it will work for a 5 speed 6 cyl e21 trans. I shortend mine by marking it cuting out the 3.1" , then I made a sleve out of some 4130 from aircraft spruce , milled it a little for a nice tight fit lined it up and tig welded it, works nice. the e21 also has sloted holes in the rear sub frame this gives you a little room for error. 323i and 320 6 same size on the trans and drive shaft.

Thanks for the info! I've updated the original post.

So, then the main question that's left is how to mount the exhaust... and what exhaust to use. Also, what exhaust header to use. Thanks.

[todor]

Bump...
I still have unanswered questions about the exhaust: do I need a E21 6-cyl exhaust manifold or will the M20B25 exhaust manifold work? Then, what lower sections can I get that will fit the US 320i? Are there any sort of performance headers? What about E30 long headers - will they fit? And the rear section - is there ANY way to mount a 323i exhaust to the US 320i body? I know the body doesn't have the dual cutouts, but the 323s that I've seen have the exhaust hanging much lower than those cutouts, so it seems like it doesn't actually NEED the cutouts. But will there be room for a muffler on the right side of the 320i?

To sum it up, I'm completely at a loss about how the exhaust side would work... starting from the engine all the way back to the muffler. Btw, I don't have to worry about emission regulations, so I don't even need a catalytic converter. Can anyone help? Thanks in advance. I need to know what to buy in advance because I don't wanna spend money on stuff that won't fit.

[Einundzwanzig]

This thread should be stickied.

[todor]

Originally Posted by Einundzwanzig

This thread should be stickied.

Amen to that

I've finally found a garage to rent where I can do the swap, so my project is about to begin! I'm still missing the 323i engine mounts and that's the main thing that's holding me back right now. But regardless of that, the first step will be to take out the old engine.

And I still have no clue what I'm gonna do with the exhaust side. I have an E30 325i parts car (the engine donor), so I'll see how much I can reuse from it in terms of exhaust piping. But if someone already knows what fits, let me know.

I'll be updating the initial post as I find out more info - either by trial and error or from fellow members' wise words

[wayfast]

whatcha paying for the garage? i need to find one to do my swap also.

for the exhaust just have it custom made. you can have it done for under $300

[todor]

Yeah I've been thinking about a custom exhaust too... may be necessary
Paying $175/mo for a 2-car garage in the suburbs (I live in the city)... but anyway, i'll keep you guys updated with my progress.

[Jester323]

Todor, feel free to come down to Portland and check out my exhaust if you want. It's not factory, looks like it was just fabbed up at an exhaust shop by a PO, but fairly simple. I'll probably be rebuilding it at some point in the future when I am ready to swap in my super eta that I'll get around to rebuilding one of these days. From what I understand, headers don't really provide too much benefit for the M20, so you could consider just using the factory exhaust manifold and have your exhaust shop build custom down pipes. I've got a header on mine with and O2 sensor that isn't plugged into anything. Likely added when it was federalized. Walloth & Nesch has stainless steel 323i headers for sale on their website. ~ $900 IIRC, pretty spendy though.

To answer your question re clutch and fly wheel, yes, any M20 clutch & flywheel should do, but I guess a bunch of E30 guys use 323i flywheels because they are lighter, significantly lighter than the dual mass flywheel for the eta motors which are something like 27lbs IIRC!

Now some ?'s that I have. I've got a K-jet M20 now, but will be installing the motronic motor & I would also like to know what to do about the fuel pumps. Are the factory pumps sufficient?

next, transmissions. I've got an M20 5-spd, but it's barely on it's last leg. The only place I can find to rebuild it is Metric Mechanic. I'm looking at about $2,200 + shipping both ways to have it rebuilt to the "Ultimate Transmission", add the E30 6-bolt guibo & have my drive shaft modified by them to use the stronger 6-bolt guibo. I don't really want to swap in an electric speedometer, so I hadn't really thought about an E30 transmission. But Matt Shaw on the Yahoo! digest suggested that I look into modifying the E30 transmission to accept the speedo cable. That's my mission today, to find out what that would entail. I'm in the process of searching here today, which is how I found this old thread.