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Meet BMW's Cayenne killers

2009-04-06 08:41
Vehicle Specs
Manufacturer BMW
Model XM
Engine 4.4L, twin-turbo V8
Power 408kW @ 5 750-6 000r/min
Torque 680Nm @ 1 500-5 650r/min
Transmission Six-speed auto
Zero To Hundred 4.7 sec
Top Speed 275km/h
Fuel Tank 85l
Weight 2 380kg
X5 M: Beauty shots
X5 M: Driving
X6 M: Beauty shots
X6 M: Driving
X6 M: Marc Surer

After months of rumours, thinly disguised spy shots and rampant denials by BMW, the first SUV M-cars (X6 and X5) are now official.

Both X6 and X5 M versions are powered by the same direct-injection, twin-turbo 4.4l V8 denoted by the fabled, tri-coloured M-badge.

Styling embellishments for these M-car SUVs are subtle, with distinctive new bumpers (featuring gills cut in the front and quad exhausts at the rear) the only distinguishing features from lesser X6 and X5 models.

Interior changes are limited to a few M-themed accents and the venerable M Drive button on the steering wheel.

M-division validated SUVs?

BMW is entirely cognisant of the possible knee-jerk reaction to dilution of its M-brand, by ushering in SUV performance cars to the most hallowed product portfolio in the blue-and-white propeller line-up.

Subsequently these SUV M-cars have to be very, very sorted - employing plenty of trick engineering to offset their weight and centre of gravity disadvantages.

From a straight-line performance perspective BMW has seemingly developed the SUV Ms to production trim with the requisite performance credentials. The 4.4l V8 features twin-scroll turbos, a new exhaust manifold and a redesigned cylinder aluminium cylinder head.

BMW, like most German manufacturers, can never pass over the opportunity to coin a new engineering term, or three.

With the X6- and X5M this debut jargon is the common exhaust emission manifold, or inter-cylinder exhaust manifold, or dual-cylinder exhaust manifold, BMW is so fond of this new technical breakthrough it kept interchanging the three terms throughout the media release...

In contemporary fashion plastic engine covers spoil much of the aesthetic appeal, plenty of clever engineering underneath though, ensuring the first forced-induction M-cars are not an embarrassment to the brand.

Nestled between the two banks of cylinders (with the turbos), the sophisticated exhaust gas plumbing allows each of the two Garret scroll turbos to be fed by a dedicated pair of cylinders, matched to fire a stroke rotation from each other, thereby ensuring a balanced gas flow to spin the turbos.

With the turbos receiving their turbine spinning exhaust gasses from both cylinder banks (instead of each turbo being fed from a single row of four-cylinders) the dual inlets are able to accommodate additional exhaust gas rerouting.

With all the forced-induction mechanicals between the V8’s two cylinder banks, intake and exhaust ducts have been significantly shortened, whilst cross-section surface area has been optimised, minimising pressure losses.

The V8’s rotational force characteristics are subsequently very linear, whereas a more conventional exhaust manifold tends to cause pressure waves when spooling up the turbocharger.

Low revving M-car power?

Power and torque peaks are hugely impressive and vastly accessible across the engine speed range. At full power, 408kW is on offer from 5 750-6 000r/min, even more impressive is the 680Nm of rotational force on-line from only 1 500-5 650r/min.

BMW M-division traditionalists will scoff at the low-engine speed peak outputs, yet the drivability coefficient is beyond doubt.

Distributing the power to all-four wheels will be BMW’s xDrive system, which has been left mechanically unchanged (BMW reckons power is still commensurate with the drivetrain parts) yet reprogrammed to provide as much rear-wheel drive bias as possible. For the doubters, ESP can be completely disabled and features M-Dynamic mode…

Doing without a H-pattern shift gate is nothing new to M-car fans, this one is no SMG or M-DCT though, it's a plain old auto...

Perhaps the biggest issue BMW will have to overcome in marketing the X6- and X5 M-cars are their availability solely with a dual-pedal transmission – and it’s not an SMG or DCT gearbox either.

The six-speed automatic gearbox does feature some clever electronics, which liaise with V8’s ECU to stall ignition on certain cylinders during peak performance gear changes - which allegedly actuates quicker shifts.

BMW promise the paddle shift operation will dutifully hold each gear right up the tachometer red-line for dynamic driving too. For those X6- and X5 M owners who are particularly keen to test their motorplan claims, and who hardly wince at mechanical abuse, the 3 000r/min threshold launch-control mode is available to be engaged when challenged by pesky hot hatches around town.

Performance claims from Munich are keen, with both SUVs (despite weighing a portly 2380kg) running a 4.7 second 0-100km/h sprint time. Top speed buffers against the 250km/h limiter, though M driver’s package models will run up to a true 275km/h.

The SUV Ms feature an economy mode too which short-shifts below 4 500r/min in daily driving (when you’re not pressing on) to aid economy. BMW claims 13.9l/100km in the EU combined driving cycle. Indeed…

Quad exhaust sprouting from the redesigned rear bumper are one of the few distinguishing styling touches.

Beyond the serious performance credentials, dynamic poise is the other key M-division engineering heritage, and considering these SUVs' largesse, it seems improbable they qualify as authentic M-cars.

Both M SUVs have been lowered 10mm and feature adjustable dampers (controlled by electronic damping control), whilst the EDC system features both normal and sport modes. The latter stiffens both the dampers and hydraulic power steering, which thankfully is not a purely electrically assisted system and has been specifically geared for the SUV Ms.

As a further affront to M-division traditionalists, these SUV M-cars are the first M-division vehicles to roll on run-flat tyres - Bridgestone’s measuring 275/40 on the front axle and 315/35 at the rear, rotating on 20-inch alloy wheels.

Hiding behind the odd, split-spoke, five blade mags, are significantly upgrades brakes.

Measuring 395mm on the front axle, and 385mm at the rear, these ventilated discs provide redoubtable deceleration.

As much as the X6- and X5 M are beyond the traditional fold of M-division expertise and brand image, one can hardly blame BMW for having gone chasing some Cayenne market share.

Expect the X6- and X5 M to go on sale locally by the fourth quarter this year.


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