This seriously quick four-door is based on the Mercedes-AMG GT 63.
Known as the RIIIx, the twin-turbocharged AMG 4.0-liter V8 has been fettled to produce a mind-blowing 1,196 horsepower and 927 lb-ft of torque on 100 octane fuel, and 964 horses/846 lb-ft of torque on 93 octane fuel. That's simply incredible. In fact, it's the most potent production package Renntech has ever offered.
As you would expect, performance is rapid. 0 to 60 mph is over in a scorching 2.44 seconds, and the big Mercedes is capable of covering the quarter-mile in 9.9 seconds at 139 mph. In-gear acceleration is strong, with 60 - 130 mph dealt with in 6.47 seconds.
It took a bit more than an exhaust system and some ECU tuning to achieve these figures, so what did Renntech do?
The RIIIx benefits from a Stage 2 turbo upgrade. Renntech's lightweight forged billet turbo wheel has a larger impeller (compared to stock) on the inlet side, along with an increased turbine trim. Naturally, an updated intercooler has been fitted, along with stainless steel downpipes and sports mufflers.
Fashioned out of 304 high-strength stainless steel, the downpipes have also been fitted with 200-Cell sport catalytic converters. Renntech says this reduces back pressure, increases turbo spooling, and improves overall performance. A crackling V8 soundtrack is a bonus. The mufflers are equally beneficial and increase the exhaust gas flow.
It doesn't end there, though. Larger carbon fiber airboxes deliver 30% more filter area, helping the engine to perform at its peak level. More durable air filters have also been fitted, along with blow-off valves.
Renntech has also treated the menacing Mercedes to an ECU and CPU upgrade. The latter allows the fuel management system to meet the increased demands placed on the engine by the turbos and tuned ECU.
Lastly, the fuel system has been upgraded to keep up with the GT 63's unquenchable thirst for gasoline. With all that power, even AMG's standard braking system may be overwhelmed. Thankfully, Renntech has upgraded the rotors and brake pads at the front and rear.
The improvements aren't limited to the engine. The limited edition RIIIx receives the Renntech A1 Aero Package, which transforms the sinister sedan into a downright threatening one. Thankfully, the exterior graphics pictured here are optional.
To complement the various carbon fiber add-ons, the car is fitted with Renntech RPS 10.2 forged aluminum wheel design, sized at 21 and 22 inches at the front and rear, respectively. They're wrapped in grippy Michelin Pilot Sport 4S tires.
RIIIx is identifiable by its decklid badging and ornamental plaques in various places. Aside from the interior and bodywork, the engine receives a special plaque signed by Hartmut Feyhl, the founder of Renntech.
Vehicles like this don't come cheap, and if you want a RIIIx in your garage, be prepared to pay. Per the tuner, the package costs $94,980 (including installation). That obviously doesn't include the cost of the GT 63 itself, which is priced around the $150,000 mark. Renntech doesn't plan on offering this package for long, so the RIIIx will certainly be exclusive.
Other tuners have also turned their attention to the GT 63 in recent months. While some examples were less than desirable, Brabus got it just right with the 930. With Mercedes-Benz planning to streamline its range in the coming years, the GT 4-door isn't expected to survive the culling and will remain a single-generation vehicle.