All hail the quad-turbo BMW M550d xDrive

The new BMW M550d xDrive is a sensible family saloon (or, ideally, a wagon), and a quad-turbocharged, M5-baiting menace. It’s an economical, discreet runaround and a 155mph autobahn demon. All things to all people? Quite possibly…

And yes, we did say quad-turbocharged. You’ll remember the old M550d, and its X5 and X6 sisters, used a triple-turbocharged six-cylinder diesel engine. Very few folks clambered out of those cars thinking ‘hmm, bit sluggish, isn’t it?’ In fact, the word ‘overkill’ came to mind, for us. 

Undeterred, BMW’s bonkers engineers have upped the blower count to four, with two low pressure turbos to get you going and then a pair of high-pressure units that come on stream once the exhaust is puffing. Like a Bugatti Chiron, then. The new turbos are smaller overall, for better response, and the results are likely to show up on a geological survey.

At 1,000rpm, you’ll already have 332lb ft at your disposal, arriving at all four wheels via a presumably bulletproof eight-speed automatic gearbox. Keep your foot in and by the time 2,000rpm is showing on the dial, you’ll have 561lb ft coursing through the tyres. That’s maintained for a further thousand revs until you get to 3,000rpm. Maximum power – a Mercedes-AMG E43-rivalling 394bhp – isn’t on tap until 4,400rpm, but by then you’ll already be moving at quite a rate.

Claimed performance is bang on the outgoing M5: 0-62mph in just 4.4 seconds for the saloon, or 4.6 seconds in the M550d Touring. The top speed is limited, rather heavily we suspect, to 155mph. 

Autobahn supremacy isn’t in doubt, then – the only diesel that really outpunches this is the tri-turbo 4.0-litre V8 found in the Audi SQ7, Porsche Panamera and Bentley Bentayga, but that’s got a whole extra pair of cylinders to lean on. Having six pots to power means BMW can squeeze 47.8mpg from the NEDC eco-test, and emit 154g/km. On paper, that matches the efficiency of a Golf GTI…

Meanwhile, M Performance trim means upgraded brakes (just as well), lower-drag aerodynamics and active steering and suspension to try and make sense of that prodigious turn of pace in the corners. 

We’re still waiting for BMW to confirm whether or not this mad Five will be sold in the UK. Its predecessor wasn’t (boo), but thanks to British thirsts for brutish SUVs, the engine did make it over here in the X5 and M6 M50d. With the political tide turning against diesel, you could be looking at its quad-turbo’d swansong, so do the decent thing, BMW…