GENEVA MOTOR SHOW
Mercedes GT saloon breaks new ground
AMG has locked down its future with its first self-engineered four-door performance car
Based on the Mercedes-AMG GT sedan concept from 2017’s Geneva motor show, the GT 4-Door Coupe is a swooping, Porsche-bashing sleek sedan.
Visually based on the AMG GT range of coupes, the GT 4-Door family is actually engineered around the same MRA modular architecture that sits beneath the E-Class, the C-Class and the CLS.
AMG engineers go-fast versions of all of them, so the chassis, suspension and powertrain development wasn’t exceptionally difficult for the brand, except for attaching some carbon fibre reinforcement in the centre and the rear end (similar to what Audi and Lamborghini have done with the R8/Huracan twins).
THE HARDCORE EDGE TO THE TRANSMISSIONS CONTINUES WITH A LAUNCH CONTROL FUNCTION.
Fitting the in-house GT styling on top of a born-to-be-Benz chassis was a bit more difficult, though, AMG has admitted. It tinkered with giving the four-door a stretched version of the all-aluminium chassis as the two-door models, but quickly abandoned that option on the grounds of rear-seat comfort and cost.
But while the concept had 600kW of power and sub-three second bursts to 100km/h, the production version takes a more predictable, practical route, using familiar V8 power and an all-new six-cylinder motor.
Although it’s not a full-on plug-in hybrid, it does adopt some of Benz’s new, cutting-edge 48V 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 that it will be available with both four and five seats and has a 395l boot (with 60l more under the floor). And it has a range of scents that can be pumped out of a bottle in the glove box, which seems important. To somebody.
The top-end version doesn’t quite hit the concept car’s claimed sub-three second time, but it doesn’t miss by much, ripping through to 100km/h in a claimed 3.2sec. The all-wheel drive AMG will reach out to 315km/h with the 470kW GT 63S version of its biturbo, 4.0l V8 engine or 310km/h with the GT 63’s 430kW output.
These motors are both familiar, but the six-cylinder motor is new to AMG, as is the GT 53 badging. The longest engine it uses this side of its ancient V12, the 3.0l in-line six crunches out 320kW power and 520Nm torque, but that’s only before the 16kW and 250Nm from the EQ Boost starter-generator chime in to add their free energy.
THE FRAMELESS WINDOWS DROP DOWN TO WIDE SHOULDERS AND HAUNCHES AND FAT WHEEL ARCHES.
It’s more complicated than that though, with the internal combustion motor being boosted by a hot-air driven exhaust turbocharger and an electric compressor adding boost at low revs. Even with the 48V 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 has 900Nm beneath its throttle pedal (and the entry V8 has 800Nm).
It’s slower than the V8 tearaways, hitting 100km/h in 4.5sec (the big brothers do it in either 3.4sec or 3.2sec), but counters by weighing less and using less fuel.
Where the heavy-hitting GT 63S weighs 2,045kg and uses 11.2l/100km, the junior V8 is 20kg lighter with the same consumption and 256g 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 S version shouldn’t just be a straight-line blaster either, with its torque peaking from just 2,000r/min and AMG insisting its air suspension and active engine mounts have been developed with comfort and cornering pace in mind.
The GT 53 hits its smaller torque peak even earlier, with the 250Nm shot from the 48V system arriving instantly, then the internal combustion engine’s 520Nm peak hitting at just 1,800r/min.
"The new AMG GT 4-door coupe blends the impressive racetrack dynamism of our two-door sports car with maximum suitability for everyday use," AMG CEO Tobias Moers says. "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."
It’s a car that has broken new ground for AMG, with obvious links to the GT coupe. 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 CLS launching in SA in fourth quarter 2018.
The stretch in the GT two-door’s chassis demanded some race-tuning thinking, including strengthening the lengthening with carbon-fibre reinforced plastics in the centre and the rear end. A single rigid subframe houses the front axle, the engine, transmission and the steering system. 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 multichamber air suspension and all models borrow the GT R’s tubular antiroll bar to reduce weight.
The new AMG, the third fully engineered and built AMG after the SLS and the GT coupes, 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 hardcore 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 AMG’s GT-badged cars have been rear-drive, the new four door uses the all-wheel drive system from the E63 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, 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.
It borrows the GT R junior 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 Coupe is the ultimate four-door sports car and the ideal ambassador for performance luxury," Daimler’s chief design officer, Gorden Wagener, says.
"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 connectivity and intelligent drive functions from the S-Class limousine, giving it solid level 2 self-driving and borderline level 3 autonomy.