N62 Z3 Part 1: Preparation & Initial Mockup

I am a big fan of convertibles, especially the BMW Z3 roadster. I have owned this 2.3 exactly a year as I write this on September 2nd. I picked it up for a very good deal, the seller thought it was a 4 cylinder and it ran like it due to a faulty intake cam position sensor. I fixed that issue the day after I bought it and a few other small things, fell back in love with the Z3 and quickly bought a 3.0i Z3 automatic and then a 2.8 Z3 manual

Somewhat ironically, once I had the other more powerful Z3's I really had no reason to drive this automatic 2.5L (despite the 2.3 badge, it has a 2.5L M52TU). So I ended up letting a friend drive it for awhile, then the A/C died on it one day and so I took it back and it bounced between my shop and my house for awhile as I decided what to do with it. I tried to sell the car - wasn't asking much but only seemed to find tire kickers (this was also at the start of the whole pandemic thing). I was parting out an N62 powered X5 at the time and realized those DME's were the same plugs and so I dug into some wiring diagrams. The X5 and Z3 wiring is surprisingly similar so I did some more research. Some people have been retrofitting N62 oil pans (and pumps) onto M62/S62 engines to fit them onto E36 front subframes - and the Z3 uses an E36 front subframe. I assumed the 6 speed transmission would be rather hard to find but a friend sent me a link to an E60 N62 with 6 speed attached for $1400 shipped. I messaged the seller a few questions and pulled the trigger. While these transmissions can be found cheaper separately, it was nice to have the flywheel included as those get very pricey on their own. The N62 and 6 speed the day I received it

Observant readers may note that this N62 has an oil dipstick, which is a nice feature seeing as the Z3 does not have iDrive (many models with N62's only got an electronic level sensor and a menu on iDrive to check it)

At this point the decision had been made - I was going to N62B44/6 speed swap my M52B25TU/automatic Z3. Have you read my intake article yet? I love the N62

Also, this 6 speed manual transmission is a ZF GS6-53, I have a GS6-37 in my S54 swapped Z3 and really love it (personally I prefer it to the Getrag 420G). While I have never driven a car with a GS6-53, I am hoping it will be similar in feel to the 37. These transmissions being similar will also play a role shortly... but for now, lets just observe how large this gearbox is, sitting next to it in the second picture is the ubiquitous ZF 320Z

Anyways, enough delicious transmission bread, lets move onto the meat of the swap. Fitment and electricity and crap like that. I had a spare E36 M3 front subframe so decided to give it the 'ol mockup. It looked pretty good. It fit, roughly anyways. The below pictures are an E60 N62B44 with E60 engine mounts sitting on a stock E36 subframe and E36 engine mounts

Things look promising. There is ample clearance between the oil pan and and subframe and everything else. You can see a little bit in the second picture the first issue I noted though - which is the angle of the engine mounts. The E36 and all models with similar style engine mounts had the mounts angling "inwards" slightly. By the time the E60 had rolled around, they moved to a completely horizontal mating surface. I thought of two things to fix this - either machine the mount arm to have an angled mating surface, or create a "wedge" type spacer on the top of the engine mount to make the mating surface flush. This ended up being a moot point as I soon discovered

I also received the engine harness I bought and wired it up. I had a spare M54 Z3 parts car so took the DME box out and mocked up some of the chassis-side wiring. The N62 DME is like the M52TU DME, in that only the X60004 plug communicates with the body. So wiring-wise, it is merely a matter of matching up the N62 DME's outputs to where they go on the Z3 M52TU. The DME even fits into the Z3 DME box with minimal modification

Appears to have plenty of room to reach into the Z3 DME box!

Unfortunately some further perusal unearthed the fact that I was lacking some earths. That is to say, some wires were cut

I got a full refund on that harness and sourced another. At some shortly after a local enthusiast was on the hunt for an M52B25TU. Hey, I have one of those. And mine runs great, plus it has low miles. This Z3 only had 83K on the odo when I bought it and 86K miles now. So we struck up a deal and I pulled the motor. I decided to also remove the radiator core support and I am very glad I did. It gives a lot more visibility to everything. Here was the car August 30th, the day I pulled the M52B25TU out

Next up was to test fit the N62...

So the first attempt was the 31st... I immediately hit some pretty major snags. I couldnt even get the engine to sit even close to a reasonable position. It was hitting the ABS module. But before any of that, I took some time to clean the engine bay. Though it was a low mile car it had a valve cover gasket leak for a little bit

Not perfect but at least now my hand wouldn't immediately become totally disgusting every time I touch the car

Below is as "in" as the N62 would get when the head was hitting the ABS module

And there it is... the head... hitting the ABS module

My initial reaction was to remove the ABS module completely. But I decided to go home and think it over. I started to think I could simply push it out of the way. I talked to someone I know who has swapped an M62 and S62 into a Z3 and he recommended I rotate it so it sits under the brake master. So Day 2 that was what I tried

I decided to remove these main supply lines and to bend some new lines once I had the ABS module set in it's final place. So I marked which one went where before doing anything

I then corrected the label on the pump

I removed the line from the front left caliper (as that was in the way when trying to rotate the pump) and also loosened all the other lines to allow them to rotate freely at the connection and then rotated the pump 90 degrees. It rotated very easily. I re-attached the line for the front left caliper, tightened the other lines and swore a lot because my hands were cut up and brake fluid burns like nothing else

This is where the ABS module sits now. The two lines that protrude out I did end up pushing in a little more, to be closer to the module itself. The engine was getting caught on them in that position

This attempt was better. But still no dice. The oil pan wouldn't quite clear the subframe. Steering rack was also being annoying. So I removed the steering rack and dropped the subframe. Then later that same day...

Engine fit roughly in place for the first time and it looks right at home. It's final position will likely be about 1" forward of this and 2-3" higher up (although the engine was also at a very steep angle in this picture, the front of the engine is much closer to it's final height compared to the rear). Although with custom engine mounts I hope to limit how high it has to sit due to hood clearance issues, not to mention firewall clearance Below you can observe how banged up the chassis got when trying to wedge this behemoth of an engine into place. Oh and also, the reason I took the photo was to show the ABS line clearance. Yes, the lines are scraped up because the engine was hitting them before I adjusted them. Fitment is really tight

So with every success comes failure. Can you spot the failure in the below images?

Maybe this video helps?

Ok in case you can't tell - I am many things, but not a photographer - the engine mount arms are too wide for the frame rails. It makes sense if you think about it - BMW installs the engines from below at the factory. So their engine mounts can be as wide as the assembled engine for clearance reasons. However, the N62 is so big (same with the M62 and S62, as far as I know) that the heads are wider than the frame rails. So it has to be installed from above into a Z3 or E36, etc... but this also means the engine mount arms are too wide to fit within the frame rails. Both sides were hitting at the same time

This issue, coupled with the need to adjust the angle of the mounts and whatnot, has led me to simply deciding to get some custom engine mounts made. As of today (Sept 2nd)... this is how it sits...

Before moving forward with the custom engine mounts, I want to talk about the GS6 transmission fitment for a moment. As mentioned earlier, I have the I6 version of this gearbox, the GS6-37, installed on my S54 swapped Z3. There is an E90 transmission brace that allows the GS6-37 to bolt to the E36/Z3 transmission crossmember and bolt in like factory. I have confirmed this fitment, as this is how mine is installed. Unverified is the belief that some E46 shift linkages will fit the GS6-37 transmission on a Z3 chassis as-is, without modification. I say unverified because it is a fairly recent discovery as far as I know, and hasn't been test fit in place yet, although measurements imply it will fit. I have bought the E46 shift linkage that is supposed to fit and the transmission brace that fits a GS6-37 to a E36/Z3. GS6-53 is physically larger than a GS6-37 but the shift linkage and transmission brace appear to be the same sizes My thinking is this - I will bolt the GS6-53 to the chassis with the transmission brace I bought, paired to the stock Z3 transmission crossmember (I have the stock auto crossmember and manual Z3 crossmembers to choose from). I will then see where the engine sits relative to the subframe and my next move will depend on how it sits at that point. I am hoping it sits in a place that allows the subframe to bolt in without interfering with the oil pan and then I can get the engine mounts made to simply set the engine in this location. That is likely very optimistic though based on some rough measurements I took prior. There is also a chance I will have to cut the firewall for intake clearance and/or get the subframe sectioned out and modified for additional oil pan clearance. Time will tell... but for now, this project is momentarily paused as I wait for parts Parts arrived! Read Part 2 Here!