E46 M3 N54 Swap Build Log


New Member
Mar 19, 2018
Camas, WA
2010 e92 335xi
Hello everyone,

I thought I'd take some time to share a build a friend and I have been (slowly) working on since the beginning of this year (2018). I actually tried to make this thread on another forum sometime during the summer, but my post ended up being eaten, and I didn't have the motivation to rewrite it.

Now I know this build might spark some controversy, (in fact, I accidentally made the album public on imgur, and within 10 minutes it had been called "absolute sacrilege") but please remember this was done as a fun weekend project, and we're wasting nobody's money but our own.

And with that, here we go...

The story begins on a cold, wet, January day when we picked up the rolling shell of a 2003 e46 m3 from some guy on Craigslist.
Here she is with all her sun bleached carbon fiber wrap and rainbow sparkle infused clear coat...oh and tasteful stickers throughout. Bet you can't guess the backstory of this one!

We had the shell, but now we needed a powertrain. The original plan was a 2JZ, which then got changed to an LS, and then finally the N54.
After sourcing an N54 and matching transmission (manual of course), the fabrication work began, but not before the initial test fit. It was quite a relief seeing how well this engine fit in the car. With all the cutouts, especially around the steering rack, lining up almost perfectly, it was like it is meant to be! Even the shifter linkage landed in the right spot.

Here's the two engine mounts we came up with. They're a two piece design with a poly bushing joining the two parts. As you might see in the background, lots of CAD (Cardboard Aided Design) was used in this process, which worked surprisingly well. (Okay, we used some real CAD too)

And here are the mounts doing their thing

Next up was the transmission mount. We found a poly transmission mount at the local auto parts store and built a mount around that. We ended up going with the shiny aluminum sitting next to our stock of inadequate steel. We'll be keeping our eye on that, and I have a feeling we'll end up replacing it with a steel version sooner or later.

About this time, I started work on the wiring/electronics side of things. We thought it would be easiest to work on the wiring outside of the car, so the entire wiring harness soon took over my attic.

And if that doesn't give you nightmares, just wait. We determined the best way to get all the additional connectors and wiring we needed would be to get an e9x body harness. So to ebay we went, and a week later we had a box containing the guts of a e90 m3.

So now we have an e46 body harness, an e90 body harness, and an n54 engine harness waiting to be morphed into one.

Cut the red wire, no the other red wire...

And now a little bit more info on the electronics. We found a DME/CAS/Key pair on ebay that were already paired. These came from a 535i (we're trying to see how many different cars we can incorporate into this build). We also have a fuse box/junction box that came with the e90 harness. An EKP (fuel pump controller) was also purchased. These should be the only (factory BMW) modules needed to get the n54 running. One of the goals was to make everything operate off of the 535 key. To do this, I repurposed two secondary air pump relays, one from the e46, and one from the e90, as terminal 15 and terminal 30 relays. These replaced the contacts in the e46 ignition switch and were signaled from the CAS. If anyone has more specific questions about how I did this, please feel free to ask.
Another goal was to retain the e46 instrument cluster. In order to make that happen, we needed a CAN bus translator. Using the fantastic work done by the posters in the e46 can bus project and e90 can bus project (not sure if I'm allowed to link), I was able to create the hardware/software needed to translate the necessary CANbus messages. These include RPM, MIL/EML, and oil and coolant temperatures. (As someone who drives a 335i, it will be quite nice to have a coolant temp gauge in the dash!) I will eventually be sharing all of the software and hardware designs I have created, but in the meantime, I will do my best to answer any questions/provide any assistance.

Now back to the engine. We did what any logical person would do and decided to run a huge single turbo. And following the theme of Built not Bought, pretty much everything about the turbo system is custom. We decided to take our chances with a no-name ebay turbo (Any bets on how long before it blows up?). I can't remember right now the exact size, but it is on the larger side of what you can put on an n54. The manifold consists mostly of Schedule 40 304 SS Weld Els.

Lots of sketchy measurements and fixturing went into making this, but in the end, everything fit together and lined up nicely. And most importantly, it all fits in the engine bay.

And yes, the turbo is held in place with Gorilla Tape, watch'ya gonna do about it?




Somewhere along the way, we had an unintentional mating between the steering rack and the oil pan...doesn't it look like a cactus?

Next up, the intake system. We of course went with one of the biggest intercoolers you can get, which meant a fair amount of trimming to the front bumper cover. The charge pipes are made from 3 inch aluminum pipe.


Well, that's where the story stands today. We are currently working on the fuel system and putting the final touches on the turbo system. Next will be the coolant system and power steering. Then we should be able to throw the wiring back in the car and start her up. It will be that easy, right?

I will try to keep this thread updated as we continue to make progress. And in the meantime, I'm happy to answer any questions and provide more specific details.

Hope you enjoyed!

Oh, and here's the album with a lot more pictures than I put in this post.


New Member
Mar 19, 2018
Camas, WA
2010 e92 335xi
Update 11/13/18

This past weekend we finished welding up the exhaust manifold and got the clutch installed.

We ended up learning the hard way how much stainless steel can move when welding. (Did I mention that this project was the first time I have welding anything of significance?)

Round 1: Lined everything up, made sure the two halves were square and true to each other, clamped everything down tightly, and got to welding the two halves together (at the turbo flange). Finish welding and notice the two exhaust flanges had moved under the clamps and were no longer parallel. Damn.


Round 2: Cut off the turbo flange, realign everything, and this time tacked the two exhaust flanges in place relative to each other, thinking there was no way it could move now. Wrong. Finish welding, cut off the tacks, and watched the two halves spring apart.


Round 3: Time for some good ol' leverage. This did the trick.


Then we got the hot side of the turbo system mounted back up to the engine and surprisingly, everything still "sorta" lined back up. It may have taken some elbow grease, but we got it.


Well, that was until we tried to put the rest of the turbo back together. The turbo flange must have twisted during welding, and now the compressor housing collides with the valve cover. So back to the chopping block...

With that disappointment, we decided to move onto something else. With the engine out of the car, it was a good time to get the new clutch and flywheel installed. We're using a Spec stage 3+ clutch paired with their lightweight aluminum flywheel. We thought this was going to be an easy task, but boy were we wrong. Has anyone ever tried to remove the pilot bearing from one of these transmissions? We tried pulling it out, which just ended up pulling out the seals and bearing race. We tried the grease method, which just ended up making a huge mess. We had to resort to using a dremel and cut off disk to get that sucker out. We managed to get it out, piece by piece, with very minimal damage to the input shaft. And that only took 6 or 7 hours to do...
But look how cool the new clutch looks!
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New Member
Mar 19, 2018
Camas, WA
2010 e92 335xi
Update 11/19/18

This weekend we summoned our inner plumbers. We got the clutch line, fuel lines, and coolant system made up.

First was the clutch. The M3 was originally an SMG model, so no clutch pedal. All of the provisions for a clutch were there, however, so fitting the OEM clutch pedal assembly was easy. The feed line to the master cylinder got attached to the existing nipple on the brake fluid reservoir. For the line from the master cylinder to the slave cylinder, we used the 335i part. The hard line section of this assembly had to be gently massaged in order for it to line up with the master cylinder in the M3. The transmission side connected together without any trouble. After bleeding the line, we now have a working clutch.

Next was the fuel system. We made this entirely custom from where the original fuel filter/pressure regulator was. We're using a 10 micron filter rated for gasoline and e85. And look at all those sleek black and red AN fittings!

A return style fuel pressure regulator capable of regulating to the 72 PSI required by the n54 was mounted to the strut tower. (Don't worry, we will be replacing the zip-ties with a proper mounting bracket very soon)

With the fuel system plumbed up, we started on the cooling system. First step was finding a spot for the expansion tank. We had both the original tank from the M3 and a tank from a 335i. The M3 tank seemed to fit a lot better, so that's what we went with. We found a spot on the strut tower that clears the hood, headlight, and charge pipe/BOV.

Most of the coolant hoses from a 335i worked without modification. However, there were two notable exceptions. One being the line that connects the expansion tank, thermostat, and heater core. We ended up salvaging the connectors from this assembly to be repurposed. The single 90* got connected to the thermostat.

The thermostat got some attention from the dremel so that the mating connector could be freely connected in any orientation.

The 3-way connector then got connected to the expansion tank and some bulk 5/8" heater hose was used to connect between the tank and thermostat.

The other modification was the main coolant inlet to the block. We cut up the stock aluminum pipe and re-welded it so that it fit around our wastegates. Unfortunately, I don't have any pictures of this, but I will try to get some for a future update.
The only remaining item to complete the cooling system is to hook up the heater core. We're waiting on a water valve, and once we get that, the entire loop will be complete.

We also started on the intercooler mount, but only got far enough to hold it in place. Right now, it's just held on with a couple of right angle brackets attaching to the core support. It will definitely be getting some more support in the near future.

And as a nice conclusion to this post, check out the new carbon fiber engine cover.
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New Member
Mar 19, 2018
Camas, WA
2010 e92 335xi
Update 3/31/19

Well, I haven't update this thread in a while, as there didn't seem to be a whole lot of interest, but today marked a rather momentous milestone that I felt like sharing anyway.

We've made quite a bit of progress over the past few months. Pretty much everything powertrain related is in the car now. We still need to make a number of brackets for things like the coolant tank, but everything is in its final-ish place and hooked up. Our goal for this weekend was to get the engine running, and I'm happy to report that we succeeded! :)



Feb 13, 2019
New England
e89 z4 35i, '92 220whp civic
Congratulations! Keep us posted with the buttoning up process also! Nice build indeed


General of the Army
Oct 18, 2016
2009 E93 335i
Nice project, moving to the N54 section where it may be more appropriate.