Mercedes' AMG performance division plans to unveil a uniquely styled and engineered, 600hp-plus four-door sedan as part of its extensive 50th anniversary celebrations.
Set to make its debut as the Vision concept next year, the new twin-turbocharged 4.0-litre V8-powered super sedan is expected to carry the name 'GT 4' when it reaches showrooms in 2019.

The GT 4 will become AMG’s third dedicated series production model line, following on from the SLS and the existing GT.

The arrival of the four-seat sedan in concept form will complement the planned unveiling of AMG’s recently announced limited-volume, F1-inspired hypercar in what is set to become a pivotal year for the brand.

Targeted at the more sporting variants of the Bentley Continental GT and Porsche Panamera, the new car, codenamed X290, is the brainchild of AMG boss Tobias Moers.

Original plans for a model in the mould of the GT 4 were first aired in a series of patent applications filed by AMG in 2012. At the time, plans centred on a long-wheelbase version of the SLS featuring two gull-wing doors and a pair of small, rear-hinged rear doors.

More recent plans for the performance four-door model subsequently became more closely linked to the current GT. But while the latest addition to AMG’s line-up will share key styling cues and elements of its mechanical package with the company’s headlining two-door, sources say it will be based on a different platform from the bespoke aluminium structure used by the Porsche 911 rival.

The basis for the GT 4 is parent company Mercedes-Benz’s modular rear architecture (MRA), as used beneath the C 63, E 63 and S 63. It has been specially modified for the GT 4, with what insiders at AMG’s Affalterbach headquarters describe as “unique” wheelbase and track width measurements.

Other dedicated features include the added use of lightweight materials within the floorpan and body structure, most notably aluminium and hot-formed high-strength steel, the adoption of which is aimed at lowering the weight of the new model to below that of Mercedes-AMG’s existing MRA-based models in the search of greater performance potential and enhanced handling characteristics.

Power for the GT 4 will come from the latest evolution of AMG’s twin-turbocharged 4.0-litre V8, already confirmed for the new E 63. The engine is tipped to be offered in two states of tune from the start of sales, with both standard 4Matic+ and S 4Matic+ models. In initial range-topping S 4Matic+ guise, the GT4's engine output is expected to top the 611hp of the new E 63 S 4Matic+.

It is understood that Mercedes’ performance car division is considering coupling the engine with a newly developed integrated starter generator (ISG). The move would not only provide it with the ability to deliver short periods of added performance via a 20hp electric motor mounted within the gearbox but also offer instantaneous start-up, with what one engineer with knowledge of the new system referred to as “seamless” stop-start qualities.

The ISG operates via a 48V electrical system, suggesting the GT 4 could adopt a moderate-sized lithium-ion battery as part of its arsenal of high-tech developments.

The engine will also feature dynamic mounts designed to suppress load changes during hard cornering and be combined with the latest version of AMG’s Speedshift MCT automatic gearbox.

The transmission will be coupled to the latest version of Mercedes-AMG’s 4Matic four-wheel drive system, which features a fully variable apportioning of power between the front and rear wheels. It will also incorporate a ‘drift’ feature that allows the driver to channel power exclusively to the rear wheels in a move aimed at promoting oversteer.

The GT 4 will be underpinned by a largely bespoke suspension system that is being developed to provide unique dynamic characteristics.

In recent years AMG sales have boomed, with sources suggesting that the recent addition of models such as the turbo 3.0-litre V6-powered C 43, E 43 and GLC 43 will help to push AMG volumes to well over 80,000 units this year.

The AMG line-up currently supports 31 models, with a plan to expand to 48 models in the future.