BMW really does stash away a good deal of its forbidden fruit in Europe, never to see the light of day in the US. The M550d xDrive is the latest vehicle to continue this trend.
The M550d xDrive is the pinnacle of BMW's performance diesel portfolio, a family we sadly do not get in the United States. Its 3.0-liter I6 engine puts out about 400 horsepower and 561 pound-feet of torque, sent to all four wheels through its all-wheel-drive system. It'll hit 62 mph in 4.6 seconds, although the sedan variant is slightly quicker at 4.4 seconds.
The most fascinating part of this car lies in the engine tech. BMW already has a triple-turbocharged I6, but in order to eke out every possible inch of performance without moving to a V8, its latest engine features not three, but four turbochargers.
It's not a traditional turbocharger setup, with each snail feeding a specific number of cylinders -- if that were the case here, each turbo would feed 1.5 cylinders, which doesn't make much sense. Instead, it uses two high-pressure and two low-pressure turbochargers.
At low revs and load, only a single high-pressure turbocharger is spinning. As the revs climb, the two low-pressure units kick in to aid the first high-pressure turbo. As the engine speed continues to rise, the last turbocharger kicks in and all four are supplying compressed air to the combustion chamber.
Of course, being one of BMW's M products -- even if it's not a fully fledged M model like the M3 or M5 -- there are plenty of other performance bits scattered about. It has a lower suspension, larger wheels and a few different options, including an interior swathed in leather and Alcantara suede. Considering how diesel isn't very well received in the US as it is in Europe, I wouldn't count on this puppy coming stateside.