Munich, Germany – Not long ago the idea of a diesel wearing an M badge would have been regarded as akin to blasphemy by the performance junkies at the M skunk works.

But diesel engines have come a long way in the past few years, and BMW’s 2993cc straight-six twin-power turbo is regarded by many as the best of the best – smooth, torquey and remarkably responsive.

Which makes it a good base for this outrageous oil-burner – the M550d xDrive, with no less than four turbochargers – two high-pressure variable-geometry units bolted straight onto the cylinder head for the shortest possible flowpath and two bigger, low-pressure turbos mounted lower down, away from the primary heat source.

The two low-pressure turbos and one of the high-pressure turbos are permanently connected; the second high-pressure hairdryer comes in at engine speeds above 2500rpm for huge top-end power. But if you boot the loud pedal at idle, automatic flaps briefly bypass the output side of the low pressure turbos so they can spool up as quickly as possible, and thus prevent turbo lag.

The results are impressive: 294kW at 4400rpm (although the engine is safe to 5400) and 760Nm from 2000-3000rpm, with 450Nm available from just off idle at 1000rpm. BMW quotes a 0-100km/h launch time for the M550d sedan of just 4.4 seconds, with top speed electronically limited to 250km/h.

All that gets laid down on the autobahn via an eight-speed Steptronic auto transmission with paddle shift, specifically set up for sporty driving, and rear-biased all-wheel xDrive, supervised by M-specific programmable drive modes, standard-fit integral active all-wheel steering and M sports suspension, with the option of Adaptive M Suspension Professional, featuring dynamic damper control and active anti-roll bars at both ends.

The M550d xDrive rides 10mm lower than the standard 5 Series on special 19 inch rims shod with 245/40 front and 275/35 rear gumballs, over M performance brakes with callipers finished in a special metallic blue.

BMW graphic shows the layout of the two high-pressure and two low-pressure turbos.

BMW’s Big Dog Diesel comes with a special front bumper with an oversized air intake, matched to a standard-fit boot-lid spoiler. Grille frame, bumper trim, side air breathers, side mirror housings and special trapezoidal tailpipes finished in dark chrome.

Contoured sports seats, with power adjustment and memory function on the driver’s side, are trimmed with a mix of fabric and alcantara synthetic suede in very dark grey, while the driver gets an M leather-covered steering wheel, aluminium pedals and footrest, and a special M instrument display.

And of course the M550d comes with the full range of 5 Series driver aids, including active lane change warning, active cruise control and remote parking, as well as the latest version of BMW Connected, that links your phone, tablet and even your smart watch to the car and the internet, reading your daily movement patterns until it knows you better than your secretary does.

Sadly, BMW has no plans for a right-hand drive version of the M550d xDrive, so we won’t be seeing it in South Africa.

IOL Motoring

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