BMW M550d xDrive (2012) - the diesel M saloon

BMW has launched its first diesel M car: the new M550d xDrive in saloon and Touring estate forms. It's part of a strategy to fill the gap between the exclusive M GmbH division cars and the top-end cosmetic M Sport trim lines with a new range of M lite: BMW M Performance Automobiles.

Developed by the engineers responsible for the M3, M5 et al, the new M550d xDrive is powered by a new high-output version of the 3.0-litre straight six turbodiesel packing not one, not two, but three turbochargers.

No wonder it puts out 376bhp and 546lb ft of torque. It's claimed to be reviver than normal turbodiesels, topping out at 5400rpm, though few drivers will need to extend it that far thanks to the sky-high torque figure.

Before you get too excited about the M550d xDrive, Brits be warned: it's not coming here. BMW GB just doesn't think there's demand for a car even faster than a 535d and knocking on the door of M5 money - and xDrive hasn't been engineered for right-hand drive.

Munich's 2993cc straight six has given a thorough going-over. There's an aluminium crankcase, piezo direct injectors squirting diesel into the cylinders at 2200 bar and three turbos.

Two are small blowers; one is activated at engine speeds just above idle and its low moment of inertia lets it build boost quickly from very low speeds. As revs pass 1500rpm, the flow of exhaust gas reaches the larger turbocharger.

From 2700rpm a vacuum-modulated exhaust flap opens allowing exhaust gas to flow past the second small turbocharger creating additional charge pressure. BMW says this allows maximum 376bhp to be developed continuously from 4000 to 4400rpm.

The addition of a third turbo makes the engine slightly heavier than a 535d, but only by around 5kg.

End result? The M550d xDrive is unsurprisingly knocking on the door of M5 performance: 0-62mph comes up in 4.7sec, top speed is limited to 155mph and it averages 44.8mpg and 165g/km of CO2.

BMW's eight-speed automatic transmission and four-wheel drive tame all that grunt and a range of M5-inspired handling mods are offered too. Springs, dampers, engine and transmission mounts are all upgraded - and the estate has air suspension on the rear axle.

There's a subtle boot spoiler and 275/30 R20 rubber to lend a menacing air to the M550d xDrive.

You can order the M550d xDrive as a Touring estate too; all the figures are within a digit or two of the saloon.

By Tim Pollard