By Samuel Ee

For the driving enthusiast who likes the capabilities of a high-performance car but does not want a hardcore, track-focused machine from the M motorsport division, BMW has created a new category of models - M Performance.

The M Performance range is characterised by extremely powerful engines and agile handling. One model is the BMW M550d xDrive Sedan.

Based on the 5 Series sedan, the M550d is buffed up with an M bodykit. But instead of the M5's 4.4-litre turbocharged V8 under the hood, there is a newly developed M Performance 3.0-litre six-cylinder inline diesel engine.

BMW diesels are already well-known for their power and efficiency. But what is unusual about this new unit is that there are three high-pressure turbochargers with variable turbine geometry to boost torque to a whopping 740 newton-metres.

By expanding multi-stage turbocharging to include a third turbocharger, BMW can generate even higher charge pressure and take the power output to the next level.

When engine speed increases to just above idle, the first of the two small high-pressure turbos is activated. As the revs increase, so does the flow of exhaust gas and the larger low-pressure turbocharger starts spinning at 1,500 rpm. Together, the small and big turbos are able to achieve peak torque of 740 Nm between just 2,000 and 3,000 rpm.

At the top end, the second small high-pressure charger contributes to even more compressed air to achieve maximum output of 381 hp.

The combined effect is one of superb lag-free response. The M550d's refinement and weight - almost 1,900 kg - may not make it feel particularly quick off the line but it is. The response to any deflection of your right foot is immediate. To rein in all that torque, the M550d has xDrive intelligent all-wheel-drive to ensure it stays surefooted wearing its 19-inch rubber.

The engine's deep reserves of power is impressive. Charging up a twisty mountain road, the M550d always seems to have a bit more oomph on tap. It's nearly impossible to make it run out of breath under most conditions and you will be able to tackle the off-camber hairpins with the same enthusiasm as the quick steering.

Along with M badges, the M550d gets the same steering wheel as the M5. Its thick rim is satisfyingly reassuring, especially in high speed curves, although it can seem to filter out some of the feedback. But there is no denying that the steering is unerringly precise.

Because all this high-speed drama is performed at relatively low engine speeds (this turbodiesel redlines at only 5,400 rpm), the cabin of this souped-up 5 Series is an oasis of calm.

This big M Performance sedan is also comfortable. The full-sized seats are ideal for any long-distance high-speed run, and the steel suspension is an excellent compromise between handling and comfort.

For acoustic entertainment, M Performance employs sound design technology to enhance the natural engine sound and pipe it into the cabin through the audio system.

With its sporty but subtle M bodykit, the M550d is a picture of understatement. The commanding yet effortless manner in which it delivers its power perfectly complements the cabin's luxury and refinement. Best of all, it sips just 6.3 litres per 100 km under the combined cycle. This M Performance car is four doors of fast, frugal fun.

samuelee@sph.com.sg

This article was first published in The Business Times.

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