That's the 850CSi - the flagship of the E31 range back in the 90s. It's an M car in many ways with Motorsport tuned and tweaked engine - S70 V12 delivering 380 BHP and 402 lb/ft or torque, M-tuned suspension, chassis, and brakes. An interesting a point to note is also the fact that each CSi comes with a VIN Number that begins with WBS ( BMW Motorsport ) and not WBA ( BMW AG ) which further emphasizes the fact that this is the closest that we'll ever get to an M8.
But .... a true blue M8 it is not. That car was nothing more than a Ferrari Killer protoype built by the M boys for testing, evaluation and board sign-off. The car was essentially a loosely patched up test-bed with no headlights, plastic windscreen / windows and probably wasn't even road-legal. Some interesting fact about this prototype was that it actually had a more powerful version of the S70 engine fitted on the 850CSi - all of 550bhp with an advanced 48 valve drivetrain design and a few other tweaks. Known as the S70/1, the engine was further improved and tweaked by the M boys / McLaren into the fabulous S70/3 or 4 going on to power the superb McLaren F1 roadcar.
Sadly, the M8 never got off from being anything more than a prototype when the supercar bubble burst and without a definitive market for such a car, BMW pulled the plug on the M8 quoting "We're just not interested in putting our name on cars like this anymore." From what is known by many, the prototype is in cold storage and will, if not already be destroyed since the 8 Series is no longer in production nor a successor being available. In many ways, it's probably the best kept secret iwithin the range of modern BMWs as no official information or data has been made available by BMW nor does it actually discusses about it despite many question and queries from car and motorsport mags.
1. Pic of the M8 prototype in testing
2. The S70/1 engine - eventually went on to power the McLaren F1 after some tweaks by Paul Rosche and team
Cheers,
VaN.