Diesel Thunder and Efficiency Arrive at M Performance



Having recently spent a day driving through Portugal in the well-executed but slightly less than inspiring BMW ActiveHybrid 5, we've now plunked our rumps into a very separate yet parallel 5 Series dimension. It's called the M550d xDrive, and instead of Portuguese hill country, we find ourselves driving over a heady combo of no-limit autobahn and essentially unmonitored idyllic two-lane Bavarian country roads. As luck would have it, the view ahead is sunny and dry.

As with any diesel phenom, the story here is not in the horsepower, which nonetheless rests at 376 between 4,000 and 4,400 rpm. You have to look at the peak torque: 546 pound-feet belting out a high-speed freight train tune between 2,000 and 3,000 rpm. That twist joins hands with the rising horsepower curve and spirals (in hugely inspiring fashion) up to a scorching rendezvous at 4,500-4,600 rpm. After which point, the two forces share a smoke, rest up, maybe chat a little to kill time while the sweat dries, and then have at it again. And again. And again. Like any active and happy young couple should do.

Yes, you can calibrate the Driving Dynamic Control system to Eco Pro mode and get fuel efficiency and CO2 emissions numbers that are (somewhat) worthy of BMW's EfficientDynamics initiative, but the environmentally friendly message has been given a distinct backseat here – even by the team in Munich. The emphasis on the M550d is on the engine's revolutionary three-turbocharger scheme. This is the first-ever diesel for public sale deemed worthy of an M badge, and the tidal wave of energy that the powerplant provides makes its 155-mph top speed governor feel like a mandatory wall for reining things in rather than like a gentle and prudent reminder.

2012 BMW M550d xDrive side view2012 BMW M550d xDrive front view2012 BMW M550d xDrive rear view

It was clear some months ago that BMW was developing a "550" diesel-powered something with an M badge attached. Now obviously official, the newly formed M Performance Automobiles division within BMW AG is here to take regular production cars up to one hairy step just shy of a full-on M tune. Having the first cluster of factory M Performance vehicles be knockout diesels is an inspired move. And that's not just for the diesel-happy Europeans who will undoubtedly gobble them up, but also for other major markets that will only get to look on for now, such as the United States.

The F10 5 Series sedan has been criticized by some as a too-maudlin step back to normalcy, a dramatic move away from the controversial and overly taut design of its E60 predecessor. We can see their reasoning, but in a way, the F10's unassuming exterior has been an ideal blank canvas to let BMW do whatever it likes under the skin, and the basic form has also responded well whenever Munich has added more air-guidance performance bits to it. This particular 5 starts customer deliveries in Germany as of May 12. An M550d xDrive sedan – were it available in the U.S. – would start at around $71,000, by the way.

2012 BMW M550d xDrive headlight2012 BMW M550d xDrive front fascia2012 BMW M550d xDrive wheel2012 BMW M550d xDrive badge

That's a lot of coin, but we had over $71,000-worth of difficulty containing our enthusiasm while talking with M Performance developers following our first top-speed strafings of the autobahns around Munich and west toward Stuttgart. Simply put, the M550d xDrive's combination of ingredients makes it, for us, the finest iteration of this 5 Series generation to date. This, despite the fact that it weighs 55 pounds more than an M5. For our money, on a larger executive premium sedan meant mostly for highway travel, nothing beats a brilliant, well boosted turbo-diesel. Those Euro execs are so lucky. Both M Performance diesel powertrain boss Nikolai Ardey and president of M Friedrich Nitschke are visibly proud of what has been accomplished with this TwinPower Turbo 3.0-liter inline six-cylinder, and with good reason.

This 3.0-liter mill, dubbed N57S ("The 'S' is for Super," says engineer Ardey), is rated at just over 125 hp per liter, making it easily the most powerful series diesel ever to rest in a BMW engine bay – or in any bay. It makes its public debut next month at the Geneva Motor Show in four models – this M550d xDrive sedan, the Touring (wagon), X5 M50d and the X6 M50d. It should be good in all four, but we figure this will be the best, just due to the physics of the sedan's comparatively lighter packaging. Ardey also hinted to us that if left unlimited, this M550d xDrive could touch 185 mph. We openly discussed with Nitschke what a great terror this engine would be in the nose of a 3 Series four-door, and all he said was that the engine could easily fit there. Oh, my.

2012 BMW M550d xDrive engine

This N57S gets its attitude from its new three-turbo setup. The basis in this unique arrangement is that of the standard TwinPower Turbo design – one smaller turbocharger with higher boost pressure ensures response times that please, while a larger turbocharger picks up at a point in the load range where the smaller turbo could start to max out. In the standard two-turbo TPT case, the boost action bypasses the small turbo at that stress point and defaults completely to the larger volume, lower pressure turbo for handling all higher loads.

With this three-turbo setup on the lower-revving diesels – still called TwinPower Turbo nonetheless – the original smaller turbo does not shut down and pass all duties to the big guy upstream when the forced-breathing going gets tough. Now, the second higher boost smaller turbo kicks in to help the original one and, under sporting conditions and high load, all three BorgWarner variable turbine geometry turbochargers are huffing and puffing together in what certainly feels like perfect sync. Maximum absolute boost pressure in this high demand state is a daunting 50.8 psi, actual applied boost being in the mid 30s.

2012 BMW M550d xDrive driving2012 BMW M550d xDrive driving2012 BMW M550d xDrive driving

Along Germany's long, straight stretches of no-limit autobahn, our M550d xDrive sedan was held back only by the onboard ECU telling us we'd filled our dance card. This 5 Series is one of those German masterworks that never feels like it's going quite that fast. The standard, full-color heads-up display of the M diesel was dancing before we knew it between 255 and 256 km/h and there was a noticeable feeling of disappointment from the throttle pedal as the engine's computer called our bluff. The car and motor wanted so badly to effortlessly show what they could really do in an unlimited world, but as it so often does, the governor had its own agenda.

There was also one of those opportunities to test the car's top-speed braking capabilities when a delivery van blithely meandered into the fast lane. They had signaled, but it was more like a meander compared to what we were doing at warp three. Even the not-terribly-special vented compound discs pulled from the 550i parts bin – 14.7-inch diameter front with single-piston floating swing caliper, 13.6-inch rear – managed to haul back in all of our momentum, winter tires howling as if offended. Yes, we were riding on less-than-ideal 18-inch Dunlop SP Winter Sport 3D tires due to understandable precautions for the winter season. (In theory, these tires are limited to 150 mph, but who's counting?). Standard M550d xDrive wheels and tires are 19-inchers, but there was a trick 20-inch set on display with Dunlop SP SportMaxx GT treads – 245/35 R20 (95Y) front, 275/30 R20 (97Y). Get these on there with some big composite brake discs, and, boy, would that put us even further into debt, albeit all the better for it.

2012 BMW M550d xDrive gauges2012 BMW M550d xDrive suspension settings2012 BMW M550d xDrive driving mode display2012 BMW M550d xDrive driving mode display

Important things like the grip of the steering wheel and feel of the shift paddles, responses of the eight-speed sport automatic transmission and war rumble of the blackened, specially designed twin-trapezoid exhaust tips all contribute to the goodness of this eminently un-diesel-like experience. Acceleration to 62 mph is quoted at 4.7 seconds – a figure which makes us laugh. A German performance testing authority publication like Sport Auto will no doubt urge a 4.5-second run or better out of this behemoth in short order.

At no point – whether at idle or under meat-hammer throttle – does the M550d xDrive sedan come across like anything but an M5 with a much better and omnipresent voice. The exhaust is created by German supplier-partner Eberspächer, and the background sound is a wondrous thing unto itself, thumping constantly up through the floor and cargo area to fill the senses. The Sport and Sport+ settings of the DDC commands throw open the bypass valves, ensuring the noise cocktail is present from take-off to v-max. At the opposite end, in Eco Pro mode and driving ever so sensibly in the flatlands, average mileage in the European cycle is said to be 37.3 miles per U.S. gallon.

2012 BMW M550d xDrive rear 3/4 view

BMW has smartly fitted an M-specific xDrive all-wheel-drive setup to this car as standard equipment. With all that torque and weight sloshing around, it's nice to have the surety of xDrive as a fundamental part of getting this big boy around every corner without having to peel off too much speed. Throughout our day, the M dampers provided a better-than-anticipated experience through the most demanding handling sections. There are denser suspension bushings employed, as well as additional anti-roll measures keeping things flatter and the steering crisper. Exits from the best curves are attacked nicely in spite of the 18-inch winter tires, with Performance Control's helpful brake-steer and power transfer to the outer rear wheel really playing an active role in the proceedings.

It would seem the perfect weather and driving conditions made us drunk with over-enthusiasm. Maybe a little, but our enthusiasm is warranted. The M550d xDrive simply doesn't seem to work as hard as the M5 sometimes does to make itself feel like a smaller and lighter car. It embraces its plus size to the best possible effect in order to optimally perform the way a 5 Series-sized car is meant to do every day. This BMW's innovative diesel powertrain could very well be the best answer to the packaging and performance requirements in the segment. Certainly for our lively test day, the M550d xDrive's tri-turbo six shows that it is far from a passing fad and more like the start of a beautiful relationship.