What is it?
Forget the sixth-generation M5 – the mighty BMW M550d xDrive is now the ultimate BMW 5-series model. At least it is in real world terms, on the sort of roads and in the changeable weather conditions we tend to encounter every day.
Spearheading a new range of so-called BMW M Performance models positioned and priced between the German car maker’s standard offerings and its more potent M division line-up , the rapid four-wheel drive diesel powered saloon establishes a lofty new standard of performance for oilburners: official figures put the M550d xDrive’s 0-62mph time at 4.7sec, standing kilometer (very much the new benchmark) at 23.7sec and a top speed at 155mph, even though it is clearly much higher without electronic regulation.
What's it like?
Granted, that’s not ultimately as fast as the new twin-turbocharged 4.4-litre V8 petrol engine powered M5 in a straight line, but it is the way it achieves these figures with such pervading potency at only moderate engine revs that makes the M550d xDrive so utterly appealing. It is a car that always feels like it has more in store, more to offer – even when scything along at triple digit speeds out on the fast lane of an unrestricted German autobahn. That, and the fact it is claimed to return 44.8mpg on the combined consumption cycle. Talk about having your cake and eating it, too.
Taking pride of place under the bonnet of the M division fettled four-door is the N57S, as BMW M division insiders like to refer to it. The highly complex and expensive to produce tri-turbocharged 3.0-litre in-line six-cylinder diesel engine – also destined for the upcoming X5 M50d and X6 M50d – provides BMW’s first dedicated performance diesel with the sort of instant-on performance and inherent entertainment value you usually only ever encounter from a high capacity petrol powerplant.
The aluminium block engine is a true technological tour de force, but despite BMW’s best efforts it still weighs 24kg more than the twin-turbocharged 3.0-litre unit it is based on. This places even greater weight over the front axle than the 535d – a car which it pips in overall output by 81bhp and 103lb ft at 376bhp and 545lb ft – the latter developed between 2000 and 3000rpm. And I never remember thinking the 535d lacks for punch.
What these bald figures fail to convey is the omnipresent energy. There’s no off-boost lethargy or waiting for it to come on song as engine speed builds. With the latest in high pressure, piezo valve guided direct injection together with a small, low interia turbocharger working in concert with a larger unit at low engine speeds to enhance the induction process, it delivers enormous shove and tremendous flexibility, and that’s just in the first couple of thousand revs.
Above 2700rpm, a second small turbocharger is engaged, providing additional boost pressure (up a maximum of 3.5 bar) and truly monumental in-gear thrust – the kind to make even the M5 feel, dare I say, a tad weak by way of direct comparison. Despite the M550d xDrive’s 1895kg kerb weight, it is heroically, epically quick.
Diesel engines aren’t supposed to respond to throttle inputs like this. At any revs, in any gear, the M550d xDrive simply flies. Pegged hard, its accelerative nature is nothing less than brutal. Nor are oilburners meant to accept revs with such unbridled enthusiasm. The new BMW engine feels totally at home operating beyond 4000rpm. In fact, it encourages you to. Peak revs are limited to 5500rpm.