They are all expensive, 2 valvers probably cheaper to maintain, I ended up putting in an '88 M6 engine. The engine fit well with stock engine mounts. Using the Getrag 280 transmission, the front portion of the driveshaft had to be shortened a bit. I think the toughest part was the wiring (need longer M6 harness), nothing a manual and a few days time couldn't fix. I also have a Conforti chip, Euro headers, M3 cats, X pipe, 745i muffler, 4.10 rear end with 55% lockup. And no, I did not do the work...

I uploaded some pictures, don't know if they made it. Try searching under "An "M7""

If you drive in the city a lot, the 2 valve 3.5 probably feels a little better torque wise. But over 3500 rpms, the M6 screams. Blew away an Impala SS the other day, pretty even with an E36 M3 on the straights on the track (still working on the curves!). Would like to drag an M3 to see what it can do...

Yeah, the modded 745s will eventually pass me (sorry, just a personal preference), but this is power RIGHT NOW to 7200 rpms!

Eric,

A well modified 745i is playing in a whole other ligua....No comparasion with any ///M car. We are talking about almost 500 HP and 650+ Nm of torque.
The ///M cars I'm playing fairly with them, every other day here around. Some times, I only take the wastegate's hose away (no mods!) just to have fun....

Regards, Afshin.
1982 745i