First Drive Review
Lately, BMW has been stretching its M division’s portfolio further than anyone would have expected a few years ago. Widespread automatic transmissions? Sure, who wants to mess with a manual anymore? Turbocharging? Everywhere, please, and we’ll bill it as “Efficient Dynamics.” And an M-powered SUV? Just what the customer wants, so let’s make two. Of all things, however, perhaps a diesel-driven M is a stretch too far. Thus, to occupy the space between the M division’s broadened portfolio and the regular BMW lineup, the M Performance line was created, with the M550d xDrive as its poster boy. We spent two weeks with the car on its German home turf.
In what has become an unfortunate hallmark of nearly every manufacturer, the 550’s model designation does not even remotely hint at its actual displacement. There is no 5.0-liter V-8 under its hood; in fact, BMW has left the V-8 diesels to Audi and Volkswagen altogether. Power comes from the well-proven 3.0-liter straight-six, here producing 376 hp, available between 4000 and 4400 rpm. Maximum torque is 546 lb-ft, served up between 2000 and 3000 rpm. Those are mouthwatering figures, regardless of what kind of fuel the engine is drinking.
To make sure this high-performance diesel doesn’t ever run out of breath, BMW has fitted it with three BorgWarner-supplied turbochargers. Yes, three. Here’s how it all works: At low rpm, a small turbocharger provides initial boost and ensures quick launches. Around 1500 rpm, a large turbocharger takes over, allowing the engine to reach its maximum torque. From 2700 rpm onward, a small, third turbo compresses the air before it reaches the large turbo. Maximum pressure for the system is 50.8 psi.
BMW says the engine was strengthened for this extra dose of power and torque that is made possible in part by an injection system that squirts fuel at 31,900 psi. (For comparison, the twin-turbo 535d’s operates at 26,100 psi.) On the M550d sedan and wagon, power is fed to all four wheels through a ZF-sourced eight-speed torque-converter automatic and BMW’s all-wheel-drive system. All this technology comes with a weight penalty, and in this case, the curb weight is about 4350 pounds.
But the chassis handles this car’s excessive weight remarkably well. The M550d remains neutral up to the limit, and there is virtually no body roll. As with the rear-drive M5 and all other xDrive 5ers, the M550d comes with hydraulic power steering, and it’s better than the soulless electromechanical setup that plagues its less powerful rear-wheel-drive siblings. Still, it’s remote and fails to live up to the BMW ideal. The car we drove was fitted with standard 245/40 rubber up front and 275/35 in the rear on 19-inch wheels; 20-inch wheels are optional.
As the power output suggests, performance is good. We estimate a 0-to-60-mph trip taking just under five seconds. No one’s complaining about that kind of straight-line talent, especially since it is accompanied by a pleasant—if artificially enhanced—snarl. The M550d really shines at triple-digit speeds, which is where you feel its extra muscle and where you realize this diesel’s atypical willingness to rev. Even accelerating from 120 and higher mph is a quick and effortless affair, making the tri-turbo perfect for long autobahn drives. Its mileage, however, is not spectacular for a diesel: The 37-mpg score in the optimistic European cycle contrasts with real-life consumption that hovers in the 20s. And dynamically, the M550d doesn’t even remotely come close to an M5. Throttle response is still diesel-like, which is to say slightly delayed. It feels more like a glorified 535d, not an M, so perhaps there was some wisdom in creating the M Performance line after all.
