Project 320ish – 1979 m50b25nv e21 gas monkey bar and grill


The end goal of this project is to have a fully functioning M50NV in the front of my car that still leaves the car comfortable and properly handles. Oh, and it has to pass California BAR standards. Turns out that a lot of things have to change to make that happen safely, up to and including a complete redesign of the drivetrain and a whole bunch of Frankenstein-ed parts being thrown together. The last few weeks I’ve been calling in favors, horse-trading parts, perusing Craigslist ads, and hitting up sales to collect pieces. It’s all been a wonderful learning experience.

The big 24 valve lump going up front weighs in at 500 or so pounds after shaving off the parts that the e21 doesn’t need, like that pesky power steering system. I sourced one locally that had two flaws. It was an automatic, and it was an e36. For those of us that haven’t read up on this swap, one of the most necessary parts of the swap is an e34 oil pan, which doesn’t come cheaply off the car unless you pull it yourself from a donor. So after waiting patiently (ish) for an e34 with a front facing sump to pop up in the yard, I got lucky.

With all of that out of the car, I got really lucky and found out that the car had been junked for a reason. On removing the transmission drain bolt, large chunks of gear the size of my thumbnail rained out. So bullet dodged there. Since it was already out, removal of the drain pan was easy and required no sawzall. Cleaned it up a bit and here we are! I also grabbed the necessary bits left from the engine, the drainpan pickup and the dipstick tube

Really that’s been most of the project so far. I’ve been having a lot of fun with compatibility of various parts from the seventies up through the mid 2000s. Through trading around and junkyards I’ve scrounged up most of the pieces from a combination of cars. Here’s a quick parts listing and a photo of how it’s all sitting for mockup in my garage.

And that’s how it sits right now. Still figuring out the front suspension will go, but the fully laden m20 and the m50 are actually within a few pounds of each other. With any luck I’ll be able to find something compatible with the early strut tubes, but I haven’t gotten there yet. I’m also at a loss as to where to put the VDO gauges. All three are just barely too big for the ashtray location on the air conditioning console, and I don’t want to block the air vent at the front with the Zender setup.

Just a small update with some more parts, a quick engineering lesson, and a proof of concept courtesy of a friend. A 2001 Z3 3.0 Roadster popped up in one of the yards. For those of us that don’t keep up with the newer bimmers, it runs off of the m54 platform, which is an aluminum block six cylinder engine with roughly the same bottom end as an m50. This one was paired with a ZF 5-speed transmission, and something special – a medium case 3.07 torsen differential.

A TORque SENsing differential operates similarly to a limited slip differential in that it allows lock to occur when one wheel travels much faster than the other or when enough torque is applied to the pinion shaft. It does this by taking advantage of different sets of gears, worms and spurs, and allowing the rear to act as one solid axle when needed. A much better explanation can be found here :…ctZopJ&index=1

In a nutshell if you can’t watch it, a worm wheel cannot turn a worm gear, but a worm gear can turn a worm wheel. It really helps to have visual reference though. Through text I don’t have any good way of explaining it further, but what you should take from this is that unless you have wheel lift, the assembly acts exactly as an LSD does, but smoother, and with more heat generated. It also doesn’t wear as quickly as a clutch does. Here’s a crappy photo of me confirming the internals that vaguely shows what I’m talking about.

So why this one? Well, it’s a medium case. Adding to that, in order to properly hang the differential with the spare tire well underneath our car one needs the rear cover off of this car. As it turns out, the output shaft flanges are interchangeable between just about any BMW medium case differential. So while I just got the 3.25 LSD, that one needed a rebuild and this one is in pristine shape. One franken-diff later, and we have all the fun of a limited slip with less maintenance and quicker, quieter operation. On top of all of that, this car also came with a ZF transmission, Z3 shifter, and a driveshaft that should lend itself to modification fairly well to hold it all together.

As I said before, there was also a matter of proof of concept. In going with the E32 rear trailing arms, the offset of the wheels is brought in from et46 to et38 or so. I’ve already confirmed that the e28 halfshafts fit together with the drive flanges on the e32. The big difference between the two is the number of teeth on the wheels for the ABS system. Happily, that won’t be a problem. Here’s the photo from the thread my friend sent me that confirms the dimensions are similar enough to work together. If this were an e28 it’d be a different story. As near as I can tell from a few hours of searching, no one has tried this combo in an e21 yet. Hopefully I’ll be successful. Cheers!

So again with the small victories and ideas moving forward, but finally got the motor on the stand and pulled/labelled the harness to start modifying it to be a manual harness. In terms of rewrapping the harness, what do people normally use that looks fairly OEM? Open to ideas.

I only got so far as removing the power steering components, harness, and valve cover last night before I had to stop to clean up the mess of coolant I made. Sorry about the photo quality, something’s going on with my phone that’s been making it worse and worse. Confirmed from the VIN on the back of the block that the block has been an automatic block all of its life. Time to change that!

Keeping with my theme of vehicular ADHD I picked up a spare cluster from a parts car while I was looking for a spare fusebox connector. Sadly there were no e21s locally that still had a fusebox, let alone a connector in decent shape. If I have to use mine I will, but I’d prefer to have the wiring more or less squared away before I drop it in the car. While I was dismantling it and staring at my still half finished dash I came up with this idea for the auxiliary gauges.

I’m not a huge fan of the zender pod, because while it has excellent placement for visual use it blocks air vents and almost never looks like it was meant to be there in my opinion. So I’ll 3D print this and fumble around a bit until I can get it to line up well with the dash, look like it belongs, and then fiberglass the lot of it to make a single cohesive piece. Who needs the seatbelt warning light anyhow?