Interestingly, the much-rumored high-performance model will probably not be badged as an M5 variant. Instead, it will likely adopt a nomenclature similar to that of the 1 Series M Coupe. Further, because of the diesel's expected high torque output, the M-tuned diesel 5 Series is likely to be offered exclusively with all-wheel drive. Following traditional BMW naming guidelines, that means the vehicle is likely to get an ungainly moniker like BMW 550d xDrive M or something similar ( TheDetroitBureau.com suggests 550dM or 550dXM as other possibilities).
The 3.0-liter tri-turbo's torque output is likely to be prodigious – perhaps in the neighborhood of 650 pound-feet (the conventional gas M5 makes 500 lb-ft), a figure more commonly associated with heavy duty pickups. Even if you've managed to wrap your gray matter around that torque surplus, you're probably still pondering the idea of a triple-turbo engine. According to TheDetroitBureau.com, the new powerplant will be based on the current 3.0-liter diesel we've come to know and love, albeit significantly modified, including a unique cylinder head. The engine will make use of a single, small turbo to help avoid lag at launch, coupled with a pair of larger twin-scroll units to augment power at speed. We hear that peak ponies will be down from the M5's 560-horsepower output, though it is still likely to stay about 500.
Predictably, the new engine is also expected to find its way into high-performance versions of BMW's X5 and X6 crossovers, both of which already offer physics-defying M models of their own.