The new 552bhp twin-turbocharged 4.4-litre V8 powered BMW M6 GranCoupé has been revealed in a series of official photographs ahead of the sleek four-door saloon’s planned public debut at the Detroit motor show in January.

Set to rival the Mercedes-Benz CLS63 AMG, Porsche Panamera Turbo and upcoming Audi RS7, the latest M-car sets out to broaden the scope of the existing M6 line-up, providing added levels of practicality and improved comfort through the adoption of two extra doors and greater rear seat accommodation. It will be produced alongside its coupé and convertible siblings at BMW’s Dingolfing factory in Germany from early 2013.

Details pertaining to UK sales are yet to be announced but officials point towards an introduction here next April at a price, they hint, will be close to £100,000.

The M6 GranCoupé is distinguished from lesser versions of the 6-series GranCoupé - revealed earlier this year - by a series of traditional exterior styling cues developed under the guise of BMW M division’s long time head of design, Uwe Weidehase.

Included is a deeper front bumper with sizeable cooling ducts for the engine bay and front brakes, altered kidney grille with twin horizontal slats and M6 identification, adaptive headlamps, widened front wheel arches, a chromed indicator lamp surround within the front wings, deeper sills underneath the four doors, aerodynamically optimised mirror housings and a carbonfibre-reinforced plastic roof panel.

At the rear, there is further M6 identification on the boot lid and a deep uniquely profiled bumper housing a carbonfibre-reinforced plastic diffuser element shaped to draw hot air away from the rear differential and a quartet of chromed tailpipes. Wheels are 20 inches in diameter – 9.5 inches wide up front, 10.5 inches at the rear. They come shod with standard 265/35 and 295/30 profile tyres.

The M6 GranCoupé is based around a high strength steel platform that boasts the same 2964mm wheelbase as the M5. As is customary for all cars wearing the revered M badge, it also receives tracks that have been widened significantly over the standard 6-series GranCoupé at 1631mm and 1612mm respectively.

The third member of the second-generation M6 line-up runs BMW M division’s twin-turbocharged 4.4-litre engine and seven-speed dual-clutch gearbox – a combination first seen in the M5 and more recently brought to the M6 coupe and cabriolet.  Power peaks at 552bhp, with torque swelling to a maximum 502lb ft on a band of revs between 1500 and 5750rpm. 

At 1950kg, the M6 Gran Coupe weighs a mere 5kg more than the M5, endowing it with a power-to-weight ratio of 283bhp/tonne – some 23bhp/tonne less than the 1795kg Mercedes-Benz CLS63 AMG, whose twin-turbocharged 5.5-litre V8 pushes out 549bhp and 589lb ft in combination with an optional performance package.

BMW claims its new super saloon is marginally faster than its keenest four-door performance car rival on the run from 0-62mph, with an official time of 4.2sec versus 4.3sec for the Mercedes-Benz. Top speed is nominally limited to 155mph. However, buyers can increase it to 189mph through an optional driver’s package, which also brings high-performance tyres.

Further straight line performance claims include a 50-75mph 4th gear time of 3.6sec and standing 1km time of 21.7sec. With standard fuel-saving functions such as stop/start and brake energy recuperation, the M6 GranCoupé’s average fuel consumption is put at 28.5mpg on the European test cycle, giving it a combined CO2 figure of 232g/km.