While we’re patiently waiting for Mercedes-AMG to unveil the GT73 hybrid with an estimated 800 horsepower, Brabus has prepared something even more intense. Meet the Rocket 900, which although doesn’t have a V12 engine like the tuner’s previous “Rocket” models, it still packs quite the punch. The latest gem from Bottrop started off as a GT63 S before getting the full aftermarket treatment.

The most important upgrade over the standard model is underneath the hood where the twin-turbo V8 engine has been heavily modified to increase displacement from 4.0 to 4.5 liters. Brabus also installed a pair of custom turbochargers with a larger compressor unit and a higher maximum boost pressure. The added oomph required extra cooling, so the tuners mounted a carbon ram-air intake on the left and right of the radiator grille.

Gallery: Brabus 900 Rocket based on the Mercedes-AMG GT63 S

The end result is an impressive output of 888 horsepower (662 kilowatts) and a gigantic 922 pound-feet (1,250 Newton-meters) of torque. However, Brabus installs an electronic limiter to protect the drivetrain by capping torque to “only” 774 lb-ft (1,050 Nm). Doing the math, the output compared to a series GT63 S has been bumped by a whopping 258 hp (192 kW) and 110 lb-ft (150 Nm).

You can imagine the significant power boost has had a huge impact on performance. The regular GT63 S is already among the fastest four-door cars out there, but the Brabus Rocket 900 takes things to a whole new level. It does 0 to 62 mph (100 km/h) in 2.8 seconds, 0-124 mph (0-200 km/h) in 9.7, and 0-186 mph (0-300 km/h) in 23.9 seconds. Brabus says it had to limit the top speed to 205 mph (330 km/h) due to the car’s high weight and to protect the tires.

Beyond the new oily bits – which also include a stainless steel quad exhaust system – the reputable German tuner also worked on the car’s design by developing an aggressive body kit with carbon fiber accents. It’s 3.1 inches (78 millimeters) than the donor car and uses bits and pieces optimized in the wind tunnel for greater aerodynamic efficiency.

The Rocket 900 sits on the tuner’s own 21-inch front and 22-inch rear forged wheels with built-in aero discs from exposed carbon. It rides about one inch (25 mm) closer to the road thanks to an air suspension developed by Brabus with selectable Comfort and Sport modes.

Brabus is converting only 10 Mercedes-AMG GT63 S “coupes” to the Rocket 900 specification and each car will come with an assortment of tweaks inside the cabin. Featuring a Stealth Gray paint, the first of the bunch has black leather and Alcantara on the inside where there’s also gray decorative stitching and no fewer than 215 parts with a body-matching color. Round off the list of upgrades are stainless steel scuff plates, carbon elements with a glossy finish, and even bespoke floor mats.

Given the extent of the upgrades, it shouldn't come as a surprise the Rocket 900 isn't exactly cheap. The Stealth Gray example pictured here costs an eye-watering €435,800, which works out to about $515,000 at current exchange rates.

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