Mercedes-AMG has built a four-door GT concept

If you fancy the Mercedes-AMG GT Coupe but need more doors and seats, well here you go. Behold the simply but confusingly named Mercedes-AMG GT Concept.

It's peppered in concept-y details. Door mirrors give way to lipstick cams. The wheels have twisted-rib spokes. Look Mum no wipers.

Yet it plainly heralds a real thing. Says Mercedes: "This four-door coupé heralds the further extension of the AMG GT family." An extension that's plainly lining up to have a go at the Porsche Panamera.

It's a five-door, with a hatch almost exactly like the Coupé's. But despite the resemblance to the GT Coupe, it's not just a lengthening job like Aston Martin did with DB9->Rapide. In fact it uses a whole different platform. See, the GT Coupe has an aluminium structure with a space-consuming bulkhead behind the two seats, and a transaxle and fuel tank position that wouldn't work with a back seat.

So instead AMG will begin with the foundation garments from the E63, and heavily adapt them, including significant proportion changes and more lightweight materials. Now of course this opens up the possibility of the E63's switchable driftable Jeckyll-'n'-Hyde four-wheel-drive system for the mad twin-turbo engine.

At the front, the Concept brings another appearance of what Mercedes calls the 'Panamericana' grille – a reference to the 300SL that won the Carrera Panamericana Mexican Road Race in 1952. All very toothy - think shark wearing teenage braces. The headlamps, side vents and tail-lamp clusters are slimmer than the Coupé's. Maybe they signal the direction of a Coupé facelift.

Mercedes has been gradually banishing feature lines from the sides of its cars this past few years, and this one is an extreme example. Trouble is, when they're gone, the surfaces themselves have to be spot-on – a fraction of a millimetre extra flab or weakness upsets the whole look. As the fractionally saggy flanks of the first-gen Porsche Panamera memorably proved.

The Concept is a big car. Those rear tyres don't look too over-sized, but they're 305/50 22s. Behind the wheels are carbon-ceramic brakes.

Nothing's said yet about the production powertrain. But even if it's part-hybrid (AMG is investigating this), all those front openings signal a whole lot of combustion from a twin-turbo 4.0-litre V8. The grilles have motorised internal shutters, opening when they need to reject heat, but closing at other times to reduce drag.

This new Concept stands as a massive popsicle-red birthday cake to AMG. Fifty years ago today, two of Mercedes' top engine men, fed up with its withdrawal from motorsport, left the company to start their own race-engine shop. Their names: Hans Werner Aufrecht and Erhard Melcher. For reasons no longer entirely clear, they added the name of Grossasbach, Aufrecht's birth village, to the initials of their company. So now you know.