With three turbochargers and four-wheel drive, the new BMW M550d is not your average 5 Series. The first of a new line of M Performance cars designed to bridge the gap between BMW's regular model lines and its full-house M products, it's also the first ever BMW M Division diesel.
The M550d will not be going on sale in the UK - at least, not in this guise, and probably not at all. That's the bad news. But we will be getting this extraordinary new engine in M50d variants of the BMW X5 and BMW X6, and the 5 Series represents an early opportunity to try it out.
It seems like the antithesis of everything BMW M, which has always previously stood for highly tuned petrol engines and rear-wheel drive driving dynamics.
But the new car is aimed at a slightly different kind of customer, someone who requires a higher degree of practicality, and doesn't want to end up on first name terms with the local petrol station personnel.
Given this, the chassis isn't tuned to quite the same degree as the latest M5, but the M550d will do 0-62mph in as little as 4.7 seconds yet claims as much as 44.8mpg on paper. And it is available as a Touring estate, as well as a Saloon.
Just not on this side of the Channel. So what exactly are we missing out on - and what on earth is this triple-turbo business about?
The M550d is powered by a 3.0-litre aluminium diesel engine that's at least nominally similar to the other 3.0-litre turbodiesels that BMW already sells. But the three turbos require not just an additional amount of plumbing but an upgrade to the unit's physical strength as well.
At 381hp and no less than 546lb ft of torque, we're told it's pretty close to the physical limits of the block - so if the concept of a highly tuned engine has sex appeal to you, rest assured this thing should do the business. It is the most powerful series production straight-six diesel on sale.
To achieve this performance in a linear fashion - that's to say without a sudden explosion of torque at some point in the rev range - a small variable geometry turbo kicks things off, followed almost immediately by the introduction of a larger turbo.
This does most of the work hard work, but at higher revs the first small turbo starts to restrict the airflow, so a second small turbo then spools up to double this up. The result is zero lag and instant response at any speed - helped along by a fast acting eight-speed automatic, specifically calibrated to the M550d's demands.
Point it up the road and put your foot down, and two things become clear immediately. First, this car is every bit as fast as it sounds - and second, it doesn't sound anything at all like a diesel. Utterly astonishingly, it actually sounds almost exactly like a petrol V8.
BMW is refusing to say exactly how it's done this - speaking loosely of component specific vibration dampening at source and a mysterious "secret" - but it is adamant the M550d doesn't have any artificial amplification (as the new M5 does, incidentally). Possibly it has some kind of active noise cancellation instead.
It doesn't really matter. What you get is a fabulous, mellifluous soundtrack with only the merest occasional hint of diesel rattle; a soundtrack you can tune in and out by changing the driving mode - the switch from Comfort to Sport is less than subtle - accompanying acceleration that is properly described as relentless.
Though power peaks 4,000-4,400rpm, the engine will rev right through to 5,600rpm, and in manual mode the 'box punches through the paddleshift changes. Yet this is no unmanageable animal: dial everything back - including yourself - and it'll potter around town like any other BMW mile muncher.
Ride and handling
While not quite extending to M5 levels, the entire M550d chassis has been overhauled to deliver a sportier drive - with everything from the rubber bearings to the Dynamic Stability Control and the optional Dynamic Damper Control getting the M treatment. Not to mention the xDrive 4x4 system.
This last has been fettled to maintain a heavy biased towards the back axle - but it still helps the M550d achieve enough traction to shrug off that thick wodge of torque, so you get greater acceleration grip and an occasional sensation that it's just saved you some trouble in a corner.
In other words, you lose little of the agile feel traditionally associated with high performance BMWs but gain the extra assurance of increased adhesion in more demanding conditions - whether that be inclement weather or hard driving. If BMW was able to offer a 4x4 5 Series over here, the Audi A6 would be in trouble.
The ride comfort is good, too - no matter which of the driving modes you have selected (standard choices being Eco Pro, Comfort, Sport and Sport+). But we're not entirely convinced by the tuning of the Servotronic variable assistance power steering, which never really seems to feel very natural.
Matching the suitably beefed-up exterior - new M550d-specific front bumper with bigger intakes, Ferric Grey detailing, rear apron, diffuser and trapezoidal tailpipe "embellishers" - the super-diesel also gets an upgraded interior.
M logos dominate, alongside special sports seats, Anthracite headlining and Aluminium Hexagon trim. Standard kit includes four-zone climate control, Xenon headlights, automatic lights and wipers, Bluetooth, USB connection and cruise control.
Economy and safety
The Saloon sprints 0-62mph in 4.7 seconds, the Touring covers the same distance in 4.9, and both are electronically limited to 155mph. Claimed combined fuel economy is 44.8mpg and 44.1mpg, respectively, with just 165g/km and 169g/km CO2 emissions. Making the M550d a supreme all-rounder.
Give it some grief and you'll swiftly see those economy claims fall through the floor - but no-where near to the extent you would in an M5; the M550d's four-wheel drive system also means less hassle should you want to drive straight through the snow to a ski resort.
Try that in its rear-wheel drive only 560hp big brother and you'll more than likely end up with the shivers. In addition to the xDrive, the M550d is fitted with a huge list of electronic safety systems, front and side airbags for the front passengers, head airbags all round, active front head restraints and tyre defect monitors.
Further improving the real-world economy is another long list of standard BMW EfficientDynamics technologies, including stop-start and that Eco Pro driving mode, which encourages you to drive more economically by showing you the journey fuel savings in real time.
The MSN Cars verdict
The BMW M5 already exhibits an astonishing breadth of ability for a hugely powerful high performance car.
What BMW has done with the M550d is sacrifice a little of the M5's ultimate performance prowess in favour of greater fuel economy, further extended usability and increased comfort, to create something that ticks so many boxes it's a wonder we aren't all prostrate at its feet and handing it the keys to the planet.
That lack of compatibility between four-wheel drive and right-hand drive means UK buyers miss out, at least for now. But if you were about to order an X5M or an X6M - or even the top spec diesel equivalents - we strongly suggest you hold fire until the M50d variants of these cars make their appearance later in the year.