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My M20 Swap


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Here it is. My M20 swap thread. I am hoping this will serve as a place for me to document my build, ask some questions, and hopefully down the road answer some questions as well.

I picked up a free '91 325i with my friend a few weeks ago and parted it out. I kept some of the parts for my self.

Right now I am just in the planning and parts accumulation stage of this swap.

There are still a few aspects of the swap that I am not clear on. I figure I have plenty of time to ready and learn.

I plan on saving some money, and parts till the end of the summer. I will have the engine brought to Morgan's Machine and Speed in Walnut Creek in

the next few months to get cleaned and resembled with a 272 cam.

Then I can spend the SF winter in a garage covered in automotive filth. Good times!

If anyone has any helpful tips and/or constructive criticism please share it! Also if you think I am missing any parts or have the wrong parts let me know. I know with a few of the parts for the swap you can use different combination's of parts.

Parts I have:

M20B25 from a '91 325i automatic

Radiator from a 325i NOT SURE IF THIS WILL FIT

318is 5 Speed (g240)

Alternator, coolant expansion tank, and all the other odds and ends

ECU, fuse box, and wiring harnesses

Custom motor mounts

oil cooler

19# injectors

A whole bunch of engine seals belts and so on

Parts I still need:

Transmission mount

Fly wheel

Fuel pump (what pump can I use with my stock fuel tank?)

Custom throttle cable

MSDS headers

272 cam

Silicon coolant hoses


WAR Chip

Windage tray

Short shift kit

LSD not the drug ; )

The first question I have is this. Do you use the fuse box from the e30 and splice in all the wires for lights and such from the original '02 wiring? That is the only thing that makes sens to me so fare.

It is going to take some time to get this thing really rolling. I will up date as soon as I have any exciting things to share.

OK some bad pictures.

My parts shed. It is cleaner now...


The bottom half of the m20 in my trunk.



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I'd suggest sticking with the stock throttle body initially, the M30 is pretty big since it's designed for a 3.5L motor and could really mess with your throttle response(aka, turn your throttle into an on/off switch)

For the driveshaft, you'll need the front 3-bolt section off an E21 or E30 drivehsaft(probably came on the 528e's and 525i's as well) and have a driveshaft shop shorten your driveshaft and add the 3-bolt front to it. Alternatively, just find an E30 driveshaft and have it shortened, it's stronger than the '02 unit.

Don't quote me, but I believe the '91 E30 318i fuel pump will work. It's still a little bit short but it's close. A universal intank pump like a walbro 255 would work too, just don't get the inline(external) version, they're noisy as fuck.

Search some of the other blogs, once spring break comes Aaron and I should make a ton of progress on both his M20 and my turbo. Blogs will be updated accordingly.

LSD, well if you had some of that you could sit in the car tripping balls thinking of how much fun it's going to be to drive/pretending to drive it. You'd become one with the car.

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LSD, well if you had some of that you could sit in the car tripping balls thinking of how much fun it's going to be to drive/pretending to drive it. You'd become one with the car.


Like this?

Thanks for the tips! I bought your engine mounts I believe... I will be getting a trans mount from you as well when they are done.

As I said before the part I am most worried about is the wiring! I hate electricity!

As fare as the M30 AFM i think it should work fine with the right tune and the 19# injectors to keep it from running to lean.

That's all down the road anyways. First is getting it in and running. Then more fast!!!

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Sorry, I read M30 throttle body. With the WAR chip I'm sure you can get the AFM to run fine. With a big throttle body like that it would turn your throttle into an on/off switch because just cracking the throttle would let in a lot more air than the stock throttle body so your modulation would go to hell.

As for the video, pretty much, but it would last a lot longer since salvia lasts only a few minutes.

Yeah those were the mounts I made, should be on their way. We're leaning towards the VW rabbit radiator since they are cheap and not too tall. What are the dimensions of the E30 radiator? I put an E30 318i radiator in my turbo project and it barely fit after a lot of cutting.

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Hmmm. Ill have to measure the radiator. i read some where that it would work...

I know many people run the M30 AFM on their modified M20's for faster throttle response. Here is a grate write up on the M20-M30 AFM conversion.


According to this guy the stock ECU will adjust it self to the new injectors and large AFM if you run a fuel pressure regulator and decrees the fuel bar below the stock setting until the ECU adjusts it's self, and then bump it back up to 3bar and let it adjust it's self again.

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The 91 318is fuel pump works like a charm. Bolts right in and its only a single pump so much less hassle. I got mine for 50 bucks off of R3v.

For the driveshaft, I just used the 2002 one (PO had it replaced. $700 receipt. Yikes!) Had it shortened and changed to a 3 bolt up front.

Wiring is so so SOOOO easy. I was a little worried going in, but an hour later I was done and though wow that was easy. If you need help with it when the time comes I could probably drive down there and help you out.

Have fun!

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Yeah, they use the stock '02 mounts. Just a little bit of trimming required on the drivers side mount. I don't have any pics of it yet, but I think it's pretty obvious once you set the rubber mount onto the metal piece. I'll get some pics up in a few weeks once I'm on spring break.

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I wish I lived closer to you guys! I do not really have any friends that work on cars and fabricate stuff, but I really love it. Never get the chance to do it. I know how to weld. I guess it does not help that I do not have my own garage/work space, and the neighbors call the cops every time I so much as look at my car the wrong way! Hate them.

My buddy has an e30 but he only ever does bolt on parts, which gets old after a while.

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