I am thinking of buying an 850Ci. What potential does this car have and what are all the mods that will help make this car faster and how much will it set me back?

Only problem I have with this car is that it is a freaking V12 and is not that fast.

It isn't designed to be FAST it is just Fffaaaaaassssstt at Autobahn speeds.

If you want to drag race with the M3 forget it. If you want to track with the M3's it can be done.

The 840 is probably easier to make quicker. For $10K or less you can supercharge it for about 450 hp at the crank.

All of them respond to changes in gearing with several choices available. Chipping the v8 or v12 bring moderate gains and are quite noticeable (depends a lot on which chip you choose).

Current V12 hot point is rebuilding as 6 liters. BUT only one sucessful builder in the states right now$$$$$.

anyone figure the DOHC head swap out yet? I have a sneaking suspicion that M54 heads can be adapted, wondering if I'm the only one who shares that suspicion.

With 4 valves per cylinder the extra displacement isn't really needed IMHO.

There was a tech session at 8 fest starring the guys doing the 6 liter V12. They didn't emphasize any movement in that direction.
The engine builder was the one that had been doing the engines at Korman. He is off on his own now.