Future plans for the 635CSi

I’ve grown quite fond of the E24 during my short tenure of ownership. It has a few problems, but it’s been well worth the effort in my humble opinion. And (other than my wife) who else’s opinion would matter?

Whats next? The next phase…those inevitable upgrades! Let’s start off with the motor. I’ve considered several options. The larger BMW V8 and V12 motors aren’t really a good fit for my intended purpose, and BMW has already built that car. (Still, it’s tempting to daydream: how about a 640CSi running an M60 with a 6 speed? Or perhaps a 654CSi with an M73B54 V12?). IMHO the older inline-6 motors and a manual gearbox are essential to my understanding of Freude am Fahren. That leaves me with two basic choices. One is a hybrid M30, customized to enhance the tractable delight of those big old M30s. The other is a turbocharged M30 (or M106).

The hybrid M30 is simply bolting together all the best parts BMW offered. The M30 came in many versions with quite a lot of interchangeability. With a little skill it’s possible to develop a bespoke version. So what’s my current planned recipe?

  1. It starts with the Euro B34 bottom end. It already has the 10:1 high-compression pistons.
  2. The single mass flywheel will be staying, of course. I’ll never give that up! In all honesty, that flywheel is the most effective performance upgrade I’ve ever done to a car.
  3. I’ll likely add an oil cooler and a windage tray to the B34 mid-sump pan.
  4. The next component will be the B35 head. It has larger ports, larger valves, a more aggressive cam and better intake manifold design. There is a slight problem with the B35’s larger combustion chambers slightly dropping the compression ratio. I’ve been lucky enough to find a skimmed head that should mitigate that snag.
  5. Likewise, I’ll keep the B35 electronics with the Bosch/Volvo EV6 injectors and AEM wideband. That 1.3 version of Motronic is a little quicker and a bit more reliable in my experience. I’ve also been doing a little research into an even newer Motronic, the 3.3.1 version. It supports a lot of extra goodies, and reacts far faster. The full sequential injection is what I’m really looking for. The individual coils and MAF are just icing on the cake.
  6. I’ve also been researching other mods. There is a rumor floating around that aircooled 93mm VW pistons and 143mm Honda H22 rods will make a hellacious stroker. I’ve also been tinkering with setting up TunerStudio for a little monitoring. Eventually, a Moats Ostrich might find its way inside the DME too.

The M106 I just bought is also a strong contender (but then I caved in and sold it). If I stumble across another, it’s a worthwhile choice. It can be a really powerful engine and the big parts fit into an E24 very easily. There are significant downsides: the turbo is not an easy fit, electronics are crude and problematic and a complete exhaust system will need to be cobbled together.