Porsche Flachbau RS by Sonderwunsch
In the footsteps of Moby Dick, the Porsche Flachbau RS by Sonderwunsch is an extraordinary one-off slantnose model that pays tribute while also marking its own path.
The specifications were requested by a Porsche enthusiast whose nearly new 911 GT2 RS was customized into a one-of-a-kind factory model by the Sonderwunsch division. Working with Manthey, they crafted a distinctive, road-legal collector's piece. Featuring a Grand Prix White paint job, the car boasts redesigned wheel arches and a bold, U-shaped contrasting graphic on the bonnet. The front design pays tribute to the legendary 935/78 Le Mans race car, also known as Moby Dick.
The Flachbau (otherwise known as slantnose) body style and the Sonderwunsch program have been closely linked at Porsche for decades: in the 1980s, the sports car manufacturer offered a spectacular modified version of the 911 Turbo (Type 930) with redesigned front wings and pop-up headlights. The design was based on the legendary Porsche 935, which dominated endurance races for years. Between 1982 and 1989, 948 examples of this modified version were sold. Even with later conversions taken into account, Flachbau models are still among the rarest variants of the 911 today.
Curiosity and intrigue in the sports car scene and the media were certainly piqued when it emerged that Porsche had registered the model designations "Flachbau" and "Flachbau RS" with the European Patent Office in May 2025. Now, the brand is revealing the secret: the reason for this patent filing was this elaborate transformation of a like-new 2018 911 GT2 RS (Type 991.2) with the Weissach Package.
Greater performance and a Flachbau look, combined with a rear wing à la 911 GT3 R Rennsport, please.
Customer
A multidisciplinary team - comprising experts from the Sonderwunsch department, Style Porsche, and development engineers from Weissach, Porsche Motorsport, and Manthey - worked on the project for almost three years. "Converting the car to a slantnose model proved to be very challenging, even though we left the drive unchanged, in agreement with the customer,” explains Alexander Fabig, Vice President Product Offering & Individualization at Porsche. "Our aim was to reinterpret the iconic look of the 935 without compromising on safety, technology or road legality. Thanks to thorough lightweight measures, this one-off car now weighs 31,6 kg less than before. That may sound unspectacular at first, but the 911 GT2 RS with Weissach Package is a sports model that is already uncompromisingly optimized in terms of weight reduction."
Responsible for the design of this Sonderwunsch project was Grant Larson, who has since retired. His involvement was a special stroke of luck; after all, he had also designed the modern interpretation of the 935 that Porsche unveiled in 2018 to mark the 70th anniversary of the legendary racing car. "The new Flachbau RS is a modern, fitting reinterpretation of the iconic 935 Moby Dick design," says Larson. "In addition to the flatter front wings, a key feature is the staggered headlight arrangement with very narrow LED units."
The color scheme also deliberately plays on tradition and modern reinterpretation: "We have combined Grand Prix White with sections painted matt black and other areas with exposed carbon fiber," Larson continues. This creates contrast, and the U-shaped contrast element at the front echoes a design feature of the Martini-liveried 935/78 - the famous "Moby Dick." The special white tone was specially developed for this one-off car. A historic 911 in Grand Prix White from the Porsche AG collection served as the reference, which the experts used to precisely match the color shade.
Purist design: the Flachbau body
The exterior reinterprets the legendary Flachbau shape of the 935. The front wings are now more low-slung and feature slatted air outlets. These louvers vent the wheel arches and reduce the air pressure within. Due to the new wing contour, the fuel filler flap and the underlying mechanism also had to be modified. The front bumper has also been completely redesigned. Subtle black flaps from Manthey underline the aerodynamic performance at the front end.
A cleverly designed lighting system replaces the standard round headlights. The three LED elements for high-beam, low-beam, and daytime running lights are arranged in tiers above one another. The individual light units are very slim: the low beam and high beam each measure just under four centimeters in height, and the daytime running lights are even more slender at less than two cm.
The factory one-off car is painted in Grand Prix White, a traditional Porsche color introduced for the 911 in 1974. Contrasting black elements provide striking accents against the exterior paintwork. Particularly eye-catching are the stripes on the bonnet and roof, which are inverted compared to the standard GT2 RS model. The center stripe and the U-shaped contrasting element are finished in exposed black carbon fiber, surrounded by Grand Prix White. The aerodiscs fitted to the rear wheels are also finished in Grand Prix White, while the brake calipers round off the sporty look, painted in deep black.
The front splitter, combined with the Manthey Kit's underbody structure, including the rear diffuser, enhances aerodynamics and ensures uncompromising performance. The carbon-fiber aerodiscs on the rear wheels reduce drag. The new rear wing with S-shaped mounts was inspired by that of the 911 GT3 R Rennsport (Type 992) but is approximately five centimeters higher on this car.
It can be manually adjusted in three positions to provide varying levels of downforce, depending on the track requirements. In the High Downforce and Low Downforce settings, the downforce on the rear axle is 2 and 3 percent higher, respectively, than on a 911 GT2 RS with Manthey Kit, with the wing in the corresponding positions. At a top speed of 340 km/h in the High Downforce setting, the Flachbau RS produces exactly 554 kg of downforce on the rear axle. The wing adjustment and the corresponding position markings are protected by a patent.
Extensive testing: at Weissach and on the Nordschleife
After the fundamental design details were defined, extensive digital validation was conducted. This included simplified crash simulations and tests to validate the airbag deployment. In addition, detailed structural analysis was conducted, particularly regarding the loads on the large rear wing. Finally, aerodynamic calculations were performed using Computational Fluid Dynamics (CFD) to further optimize the overall design. It was only after these virtual tests were successfully completed that the go-ahead was given to produce new tooling to manufacture the modified components.
This was followed by technical validation of the individual components. The new rear wing was subjected to extreme vibrations on a hydropulse test rig, similar to the vibrations encountered - albeit to a lesser extent - during road use. In addition, the experts also tested its static load-bearing capacity using sandbags.
"On the Nordschleife, it becomes immediately clear how cleanly aerodynamic concepts work," says Porsche test driver Lars Kern, who drove the sports car on the famous track. "The Flachbau RS remains extremely stable and precise even at very high speeds. This is exactly the kind of feedback needed in order to validate such a radically altered body design."
A total of three test vehicles were built to conduct further validation tests in facilities such as lighting and wind tunnels, as well as during real-world road tests. Numerous test drives at the Mendig airfield, 50 laps on the Nürburgring-Nordschleife alone, and endurance tests at the Weissach site combined to simulate a load on the rear wing equivalent to about 150,000 kilometers of customer use.