The BMW 5 SeriesM550d is our first encounter with the company's new M diesel engine, which uses the expertise of the M division (creator of the M3 and M5) to offer levels of performance and sporty handling well beyond that offered by the simple M Sport packages.
It uses a new version of BMW's 3.0-litre, straight-six turbodiesel engine now with three turbochargers, 376bhp and a whopping 546lb ft of torque.
A small turbo kicks in just above idle, followed by a large one above 1500rpm. At 2700rpm a second small turbo joins in to take the increasing load off the main unit, helping provide power right up to 5400rpm. The engine has been strengthened to cope with the new forces within.
All this power is fed through an eight-speed automatic gearbox and a four-wheel-drive system, which sends drive to the rear wheels the majority of the time.
What's the BMW M550d like to drive?
Extremely enjoyable. The engine responds instantly, and the transitions between the three turbos' contributions are undetectable. The combination of eight gears and an unusually broad spread of power (for a diesel) makes the M550d a car that's happy to be driven both effortlessly or hard the latter helped by the gearbox's quick but smooth shifts.
The M550d can blast from 0-62mph in an astonishing 4.7 seconds, yet it can average 44.8mpg and emits just 165g/km of CO2. All this is accompanied by the most un-diesel-like soundtrack we've ever heard. As in the BMW M5, the stereo system is used to emphasise some aspects of the sound and reduce others. At times you'd think you were driving an Aston Martin, especially when Sport mode is selected.
What's the BMW M550d like inside?
Much as you'd expect: sporty seats, textured aluminium (instead of wood), and a chunky leather-trimmed steering wheel set it apart from a regular 5 Series.
Should I buy one?
Unfortunately you can't, because BMW is unable to combine the four-wheel-drive xDrive drivetrain with right-hand-drive models. A rear-drive-only version could be built, but as yet BMW sees no business case for it in the UK.
Vital stats in these cars are 0-62mph in 5.4 seconds, 37.7mpg and 199g/km of CO2 for the X5, while the X6 travels from 0-62mph in 5.3 seconds, has average economy of 36.7mpg and CO2 emissions of 204g/km.
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