BMW's engine range for the X5 primarily focuses on diesel units and comprises the 25d, 30d, 40d and 50d. All but the 50d, which displaces 3.0 litres, are 2.0-litre engines.

A 4.4-litre twin-turbocharged petrol V8 is also offered in 50i variants, for those seeking the most refined of the X5s. To date we've only tested the 30d, 50d and 50i.

With the transmission in manual mode, with Sport+ engaged, it won't change up when you hit the limiter

The 3.0-litre diesel variant of the new X5 is much improved compared to its predecessor, its clatter and growl usurped by a subtle background hum. Lots of low-rev urge and the eight-speed auto gearbox’s excellent anticipatory skills make for authoritatively brisk and effortless performance that, at lower speeds, shades the petrol 50i for easily accessed power.

The 50i provides a 4.4-litre V8 coupled to an eight-speed paddle-shift transmission. It’s an engine familiar from the last X5, now with a sharper performance and economy mix. Power climbs 10 per cent from 401bhp to 444bhp while torque rises 37lb ft to 479lb ft to shave half a second from the 0-62mph time, which falls to 5.0sec. Economy improves a little, too.

Yet despite this potency, and the traction to make good use of it, this ultimate petrol X5 is not the fastest thing off the line. Engine and transmission need a frustrating few moments to absorb your commands before launching the BMW with the power you’d desired moments earlier.

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It’s a pause that appears when you’re on the move at lowish speeds, too, although switching to Sport mode enlivens the drivetrain. The engine sounds good, too, providing a satin V8 beat that turns impressively muscular when the throttle is sunk deep.

BMW’s tri-turbo diesel has it all to do in the 2.4-tonne X5. Given the choice, we wouldn’t have picked such a heavy, unaerodynamic machine for our first test acquaintance with the powertrain codenamed ‘N57S’. But there’s no right-hand-drive version of the all-paw 5-series in which it features and so, for now, no way for us to find out what kind of numbers it might produce when less encumbered.

Even in the X5, the motor is formidable. It feels every bit as responsive as a typical twin-turbo oil-burner and every bit as smooth. Its 546lb ft is the obvious attraction. It’s available from 2000rpm to 3000rpm and is delivered undramatically enough to make you wonder if you’re really getting everything you’re being promised.

Our numbers suggest that you are, though. The X5 M50d will rush from 30-70mph in fourth gear more quickly than an Audi R8 V10. It may never feel like it’s pinning your ears back, but it’s very brisk indeed. The ZF eight-speed automatic gearbox is the perfect partner for the engine, too, picking a ratio early when you flex your right foot, allowing the motor to pull through the mid-range and making back-road overtaking and motorway slip-road acceleration absurdly easy.

We don’t doubt that this would be a true 160mph car, given enough space and a means of disabling its top speed limiter. But what impresses most about the engine is its willingness to rev. You don’t encounter the redline until 5500rpm, and neither do you feel power tailing off significantly before the cut-off presents.

BMW has made sporting diesel engines before, but here it has achieved quite a coup: a truly flexible, gutsy six-pot that you’d happily take instead of most V8 TDIs.

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