Porsche and Manthey Build a Slantnose One-Off on the 991.2 GT2 RS

• Flachbau RS is a single, road-legal one-off built on a customer’s 2018 GT2 RS

• New rear wing generates 554 kg of downforce at 340 km/h

• Lightweight modifications removed 31.6 kg from the car

Porsche unveiled the Flachbau RS, a single, road-legal one-off built by the automaker’s Sonderwunsch personalization department in collaboration with Manthey, during Monterey Car Week in California. The car began as a customer’s own 911 GT2 RS (Type 991.2) with Weissach Package, delivered in 2018, and was transformed into a slantnose tribute to the 935/78 endurance racer nicknamed “Moby Dick.”

The project took nearly three years and involved a team from Sonderwunsch, Style Porsche, and development engineers from Weissach, Porsche Motorsport and Manthey. The customer’s drivetrain remained unchanged; Porsche did not restate the GT2 RS’s output figures in the release.

New Bodywork and a Flatter Front End

The Flachbau RS gets flatter, more low-slung front wings with slatted air outlets that vent the wheel arches, along with a redesigned front bumper and black aerodynamic flaps from Manthey. A new lighting system replaces the standard round headlights with three tiered LED elements for high beam, low beam and daytime running lights. The high and low beam units each measure just under four centimetres in height, with the daytime running lights under two centimetres.

The car is finished in Grand Prix White, a Porsche colour dating to 1974, with contrasting matte black sections and exposed carbon fibre on the centre stripe and the U-shaped element on the bonnet. Grant Larson, the now-retired designer who also created Porsche’s 2018 tribute to the 935, led the design.

Wing Delivers 554 KG of Downforce

A new rear wing, with S-shaped mounts inspired by the 911 GT3 R rennsport (Type 992) and mounted roughly five centimetres higher than that car’s, can be manually set to three fixed positions. In the High Downforce and Low Downforce settings, the wing produces 2% and 3% more downforce on the rear axle, respectively, than a 911 GT2 RS fitted with the Manthey Kit at equivalent wing positions. At a top speed of 340 km/h in the High Downforce setting, Porsche says the Flachbau RS generates 554 kg of downforce on the rear axle. The wing’s adjustment mechanism and position markings are patent protected, alongside the “Flachbau” and “Flachbau RS” names Porsche filed with the European Patent Office in May 2025.

A front splitter, the Manthey Kit underbody, a rear diffuser and carbon fibre aerodiscs on the rear wheels complete the aerodynamic package.

31.6 KG Lighter

Lightweight modifications cut 31.6 kg from the car. Porsche removed the Porsche Communication Management infotainment system, the audio system, and most sound-deadening material and floor coverings from behind the seats, replacing them with exposed, painted metal and a leather storage compartment. Wiring no longer in use was removed entirely, and the remaining harness is covered only by protective sheathing.

The carbon fibre bucket seats carry embroidered “Flachbau RS” lettering on the headrests, and a gold Sonderwunsch badge marks the passenger side of the dashboard. A removable “emergency box” now houses the warning triangle and towing eye required for road use.

Testing at the Nordschleife

Porsche validated the design through crash and airbag simulations, structural analysis of the wing mounts, and CFD aerodynamic modelling before building three test vehicles. Testing included runs at the Mendig airfield, 50 laps of the Nürburgring-Nordschleife, and endurance testing at Weissach equivalent to about 150,000 km of customer use. “The Flachbau RS remains extremely stable and precise even at very high speeds,” Porsche test driver Lars Kern said.