The Mercedes-AMG GT63 S has targeted the Porsche Panamera Turbo in power, shape and customer, but how do the supersaloons stack up when side by side?

The Mercedes-AMG GT 4-door was not the car industry’s best kept secret before its recent reveal at the Geneva motor show. Shown in concept form and spotted in its test mule guise regularly over the previous 12 months, the GT 4-door has been developed by Mercedes-AMG to offer the Mercedes-AMG GT Coupe’s looks and performance in a more practical package.

One look at the spec sheet though and you’ll notice the 4-door comprehensively outguns its two-seater sibling in terms of performance and capability. Not only this, a closer look at the two also reveals that despite the shared nameplate and similar styling, the GT 4-door is based not on the aluminium space-frame chassis that underpins the GT coupe, but the MRA platform that Mercedes uses for the majority of its more humble saloons. So the question begs to be asked why Mercedes built the GT 4-door at all, especially when the CLS four-door coupe essentially does the same job. The answer might have something to do with the Porsche Panamera.

> Click here for our 2018 Geneva motor highlights

What started out as a strangely proportioned oddity, the Panamera has now come of age. Based on VAG’s new MSB platform co-developed by Porsche and Bentley, the second generation Panamera is now an important technical statement for the whole Volkswagen group. This is what Mercedes-AMG engineers have tasked themselves with usurping in a class that now sits above traditional super saloons like the E63, M5 and RS6. Here we’ll dissect the numbers before the AMG GT 4-door and the Porsche Panamera inevitably get pitched against each other on the road and track.

The two cars should also sit closely in terms of pricing. Mercedes-AMG has confirmed a starting price of over six-figures for the GT63 and GT63 S models in the UK, right in line with the Porsche.

The chassis

A key question asked when the GT 4-door was revealed was why Mercedes didn’t utilise the lighter, aluminum space-frame chassis that underpins the actual GT Coupe. After a conversation with Mercedes-AMG at the 2018 Geneva motor show, we now have a more transparent understanding of the thought process behind this decision.

One of the major reasons was Mercedes-AMG’s desire to fit all-wheel drive. The GT Coupe and Roadster both utilise a chassis designed to fit a transaxle dual-clutch gearbox mounted on the rear axle connected to the engine via a solid torque tube. This is done for improved weight distribution, and the ability to mount the V8 engine further back in the chassis giving the GT its classic long bonnet look and front/mid-mounted engine status.

> Click here for our look at the AMG GT63 S

Unfortunately, the task of then routing that power back to the front wheels is difficult when combined with a rear-mounted gearbox, as the power has to run back up a secondary driveshaft to reach the front axle. Manufacturers have overcome this problem before, Nissan notably with the GT-R, but then all manner of packaging problems arise, not least the need to raise the engine to allow the requisite components to reach the axle. Ferrari also encountered a similar issue in the FF and GTC4 Lusso, but rather than fitting a second driveshaft, it instead mounted a smaller, secondary gearbox to the front of the V12 engine, connected to its own two driveshafts.

In light of all this, Mercedes decided to base the AMG GT 4-door on the more typical MRA platform, with the engine and gearbox both front mounted and able to be more easily adapted to all-wheel drive. Mercedes-AMG has made the GT 4-door the lowest and widest MRA-based model yet to try and emulate the Coupe’s style, but you’ll see the crucial dash-to-axle ratio is much closer to normal Mercedes saloons and therefore lacks the Coupe’s dramatic proportions.

Porsche on the other hand had the chance to design and develop the Panamera’s MSB chassis from scratch, giving its engineers more freedom and flexibility. You can see this in the Panamera’s wide, low stance, something it shares with the new Bentley Continental GT and its upcoming four-door Flying Spur sibling. Here the Panamera’s V8 engine is mounted further back in the chassis as compared to something like the Audi A7 Sportback, which despite the similar shape and common parent company, is based on the MLB-evo platform which underpins everything from an Audi A4 to the Lamborghini Urus. Being based on the larger MSB platform, the Panamera gave Porsche a more specialised base to work from in its development, providing a slight leg-up against the Mercedes-AMG GT 4-door.

Mercedes-AMG GT four-door revealed at Geneva

The powertrains

Let’s start by acknowledging that the specific models of this car are not perfectly lined up for this comparison. For the sake of equality, we’ll look at the most powerful, non-hybridised variant of each model – the Mercedes-AMG GT 63 S and the Porsche Panamera Turbo fitted with the Sport Chrono pack.

The Mercedes-AMG GT63 S 4-door shares the same basic 4-litre M177 twin-turbocharged V8 engine as the E63 S. The all-aluminium V8 is a 48v, ‘hot vee’ unit that mounts its turbochargers between the cylinder banks to increase throttle response times. This technique has been quickly adopted by many premium brands, thanks to its inherent performance and packaging advantages. Producing a maximum power output of 470kW between 5500 and 6500rpm, the GT has a 20kW power increase on the E63 S and is a solid 65kW up on the Porsche. Torque is rated at 900Nm produced between 2500-4500rpm another big 130Nm gain on the Porsche.