When I first went to see this car, I immediately created a project plan. My plans are typically pretty mundane; there are so many ways to waste money on cars. I always try to stay within my means, feet firmly on the ground. I’ve seen far too many CL projects that just ran off the rails. Primarily, I strive not to exceed the net sales value of the car. Once I’ve gotten that budget estimate, I can narrow down the possibilities. Depending on the car, then I determine which way I think the project will go. Should I make it a decent daily driver, or restore it like-new? If it’s a little ratty, should I modify it instead? If the choice is ‘mod’ instead of ‘resto,’ how far should it go?
BMW is – first and foremost – an engine manufacturer. They’d been designing aeromotors long before they started with motorcycles & cars. It’s their middle name, literally. In my small way, a few of my fondest automotive memories are the result of their vaunted inline-six motors. Much of that mystique is due to the M30 “Big Six” motor. Basically just a modified M10 four-cylinder (fortified with 50% more cylinders), BMW produced them over a quarter century. They provided much of the basis for BMW’s racing successes in the 70s and the resulting sales successes in the 80s. These motors are still not to be underestimated, even today.
Of course, I didn’t want just any old M30…I wanted the best version I could afford. I decided to ignore the expensive racing variants (the Motorsport M88, M90 and S38) due to high maintenance costs. Two of the more pedestrian M30 motors stand out. The European version of the M30B34 was significantly more powerful than the US version. It was built for higher speed European highways, more demanding customers and sloppier emissions regulations. This motor was bored & stroked with higher compression pistons, hotter cam and a better-flowing exhaust system. It was also typically fitted with an oil cooler, a single-mass flywheel and a heavy-duty drivetrain. Nicknamed the “dirty M30” due to a lack of any emissions controls whatsoever, it’s more powerful and a lot more fun than any of the US versions. Eventually, BMW retired this motor and replaced it with a “world-model” engine, the M30B35. This version had better flowing manifolds, a more efficient head casting with larger valves, and an updated version of Bosch Motronic. It was better in many ways than the earlier Euro motor and almost as powerful. It’s also cheaper & far more common; the Euro motor was never offered for sale here because it couldn’t pass long-term emissions testing in the USA. So my project would have to have one of those two…but just to get it back on the road. I’ll be building my own motor later, combining the best of these two motors into a naturally-aspirated beast!
So how did it turn out? I patiently waited to find the proper donor. I passed up a Euro E23 735i because it was a flood victim, the seller wouldn’t negotiate, and I didn’t have enough cash. Then I stumbled across a complete ’82 Euro 635CSi right next door in Ohio, desperate for redemption. In this case the “dirty” moniker was more than apt…this car had been trapped in a freshwater flood, totaled by an insurance company, auctioned for scrap, then left in a field to rot. It was a moldy rusted-out disaster, fit only for mice. The powertrain was a hidden treasure…certainly good enough to bring it back to life. It was fitted with one of Getrag’s toughest transmissions: the excellent 265/5 wide ratio 5-speed box. The only mechanical disappointment was the differential…unfortunately an open non-locking type. Oddly, it appeared to be a 188mm ring in a 210mm case. Never seen anything like it from BMW. I ended up finding a far superior diff somewhere else. Read all about that process here.
I also lucked out with a few choice parts that came along with these cars. I couldn’t use them, so I sold them to fund the project. The ’86 donated a full OEM M5 exhaust, M5 quad-piston front brakes and the M5 radiator, among other pieces. I sold a lot off the ’82 Euro as well: desirable manual transmission parts, an original Becker stereo, the rare trunk-mounted spoiler, a few decent trim parts like windows, rear seats & mirrors. I also scrapped the chassis & wheels.
I did keep a few of the tasty upgrades. I lucked out on the ’86 because it already had Bilstein Sport struts/shocks, Ireland Engineering springs & M5 sway bars. I also rebuilt the Euro’s front calipers and installed them on the ’86 to replace the M5 parts I’d sold off.