GENEVA MOTOR SHOW: Mercedes-AMG's Panamera basher unveiled

Based on the Mercedes-AMG GT sedan concept from last year's Geneva motor show, the "GT 4-Door Coupé" is a sleek new rival for the Porsche Panamera and Maserati Quattroporte that should be on sale in Australia around March 2019.

But while the concept boasted 600kW of power and sub-three-second bursts to 100km/h, the three production models announced in Geneva took a more predictable and practical route, two using familiar V8 power and one an all-new six-cylinder motor.

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While it's not a full-on plug-in hybrid, the GT 4-door does adopt some of Benz's new, cutting-edge 48-volt mild-hybrid electric boosting — but only on its entry-level straight-six version.

AMG isn't confirming its overall dimensions or its footprint, but it admits only the GT 4-door will be available with both four and five seats and has a 395-litre boot (with another 60 litres under the floor).

And it has a range of scents that can be pumped out of a bottle in the glovebox, which seems important. To somebody.

Fast, all three

The top-end GT 4-Door Coupe 63 S doesn't quite hit the concept car's sub-three-sec time, but it doesn't miss by much, ripping through to 100km/h in a claimed 3.2 seconds.

The all-wheel drive AMG will reach out to 315km/h with the 470kW GT 63 S version of its biturbo 4.0-litre V8 engine or 310km/h with the GT 63's 430kW output.

These engines are both familiar, but the inline six is new to AMG - it will gradually seep out through the AMG line-up starring with the CLS — as is the GT 53 badging.

The longest engine AMG uses this side of its ancient V12, the 3.0-litre inline six crunches out 320kW of power and 520Nm of torque, but that's only before the 16kW and 250Nm from the EQ Boost starter-generator chime in to add their free energy.

It's more complicated than that, though, with the internal-combustion motor being boosted by both a hot air-driven exhaust turbocharger and an electric compressor adding boost at low revs.

Even with the 48-volt power system kicking in twice (with the starter-generator and the electric compressor), it doesn't top the most-powerful V8 for torque, because the fastest GT 4-Door Coupé has 900Nm beneath its throttle pedal (and the entry V8 has 800).

It's slower than the V8 tearaways, hitting 100km/h in 4.5 seconds (the big brothers do it in either 3.4 or 3.2 seconds), but counters by weighing less and using less fuel.

Where the heavy-hitting GT 63 S weighs 2045kg and uses 11.2L/100km, the junior V8 is 20kg lighter with the exact same consumption and 256g/km emission figure.

Even cylinder-on-demand technology, to shut down four cylinders when the driver is in Comfort mode and the car is cruising with low torque demands, doesn't seem to help too much.

The GT 53 weighs 1970kg and uses 9.1L/100km, emitting 209g/km of CO2 on its way to a 285km/h top end.

The GT S version shouldn't just be a straight-line blaster, either, with its torque peaking from just 2000rpm and AMG insisting its air suspension and active engine mounts had been developed with comfort in mind as well as cornering pace.

The GT 53 hits its smaller torque peak even earlier, with the 250Nm shot from the 48-volt system arriving instantly, then the internal-combustion engine's 520Nm peak hitting at just 1800rpm.

Australian-bound

All three versions of the GT 4-door could show up in Australia. Consider the 53 and 63 S virtual certainties, while there is still some debate within Mercedes-Benz Australia/Pacific about fitting the standard 63 into the line-up.

Pricing is yet to be locked down, but it will be higher than high-performance four-door models such as the E 63 S and below the S 63, as well as the GT Coupe.

So that suggests a starting price beyond $200,000 and a top-out of around $300,000. But that is pure guesswork for the moment.

"The 63 S is a no-brainer for us and we are just looking at where the 63 and 53 fit," said MB A/P product communications manager Jerry Stamoulis.

"The amount of Panameras and Maseratis that are selling certainly means there is a market for this car, otherwise we wouldn't be considering it, or considering three models."

AMG CEO Tobias Moers said: "The new AMG GT 4-Door Coupé blends the impressive racetrack dynamism of our two-door sports car with maximum suitability for everyday use."

"It has a unique way of embodying our brand core, 'Driving Performance' and with its systematic configuration it will attract new customers for Mercedes-AMG," he hoped.

Not so GT

The GT 4-door is a car that has broken new ground for AMG, with obvious links to the GT Coupe, in particular. It gives Benz a higher-priced four-door that is about the same size and does about the same job at about the same speed as another Benz that uses aggression, swoopier styling and also calls itself a 'coupe' - the just-launched CLS.

However, the basis of the GT 4-door is not the GT coupe architecture, but Benz's ubiquitous MRA rear- and all-wheel drive underpinnings as seen under the C-Class and E-Class.

It's also been given all-wheel steering, turning in the same direction as the front wheels at high speed and in the opposite direction at low speed.

While the six-cylinder GT 53 uses steel springs and adjustable dampers, the V8s use multi-chamber air suspension and all models borrow the GT R's tubular anti-roll bar to reduce weight.

The GT 53 and GT 63 models use 355/45 R19 tyres at the front and 385/40 R19s at the rear, while the GT 63 S bumps that up to 265/40 R20 at the front and 295/35 R20 at the rear.

The new AMG shares its little brother's twin domes in its long bonnet. All three powertrains punch their drive through nine-speed automatic transmissions, all governed by AMG's own clutch pack for harder, faster shifting than the standard Benz models can manage.

The hard-core edge to the transmissions continues with a launch control function, dubbed Race-Start by AMG, and a Drift mode that takes advantage of the rear-biased nature of the all-wheel drive system.

While all of AMG's GT-badged cars have been rear-drive, the new four-door uses the all-wheel drive system from the E 63 S AMG, with an electro-mechanically controlled clutch connecting the permanently driven rear axle to the as-needed front differential.

It constantly varies the front-to-rear torque split, which is a job made easier by its electronically locking rear differential on the (more expensive) Dynamic Plus version.

Its standard brake package will feature six-piston front callipers and a pair of single-piston floating callipers at the rear-end.

Designer coupe

It borrows the GT R supercar's radiator shutters, too, to give it better real-world aero efficiency, while the frameless windows drop down to wide shoulders and haunches and fat wheel arches.

"The new AMG GT 4-Door Coupé is the ultimate four-door sports car and the ideal ambassador for Performance Luxury," Daimler's Chief Design Officer Gorden Wagener said.

"It embodies a symbiosis of emotion and intelligence with breathtaking proportions and a puristic, surface-oriented design with sensuous shapes. It is both hot and cool at the same time."

It borrows heavily from the GT's interior design, particularly its dash layout, with turbine-like vents and two high-resolution 12.3-inch digital displays across the wide cockpit.

It uses the all the connectivity and Intelligent Drive functions from the S-Class limousine, giving it solid Level 2 self-driving and borderline Level 3 autonomy.