There are custom cars, and then there are cars that turn a customer request into a full-blown engineering program. Porsche’s latest Sonderwunsch project belongs firmly in the latter category: a road-legal, factory-built 911 GT2 RS transformed into a dramatic slantnose machine inspired by the fearsome Porsche 935/78, better known as “Moby Dick.”

The brief, apparently, was wonderfully straightforward: more performance, a Flachbau look, and a rear wing with the visual theater of the 911 GT3 R rennsport. What followed took nearly three years and brought together Porsche’s Sonderwunsch division, Style Porsche, engineers in Weissach, Porsche Motorsport, and Nürburgring specialist Manthey. The result is called the Flachbau RS, and it is a genuine factory one-off rather than a bodykit special.

At first glance, it looks like something that escaped from a very alternative Porsche timeline. The familiar 991-generation 911 GT2 RS shape has been stretched, flattened, and sharpened at the nose. The front fenders sit lower, the standard round headlamps have disappeared, and the body adopts the kind of long, low-slung visual attitude that made the original Moby Dick so memorable. In Grand Prix White, with black exposed-carbon elements and a bold U-shaped graphic over the hood, this car does not merely reference racing history. It wears it openly.

The nickname comes from the Porsche 935/78, an extreme racing evolution of the 911 Turbo-era 935. Its dramatically elongated tail gave it a whale-like silhouette, while its race-bred engineering helped turn it into one of the defining Porsche competition cars of the late 1970s. Porsche says the 935 won the World Championship for Makes four consecutive times and scored major success at Sebring, Daytona, and Le Mans.

“Moby Dick” has always represented the point where Porsche’s rear-engine sports car stopped trying to look polite. It was wide, long, brutally purposeful, and built around the idea that speed could dictate shape. That same philosophy runs through the Flachbau RS, even if this new car begins life as a street-legal 911 GT2 RS rather than a purpose-built endurance racer.

The slantnose connection is important, too. Porsche offered the original 930-generation 911 Turbo Flachbau in the 1980s, borrowing its flattened front-end look from the racing 935. Between 1982 and 1989, Porsche sold 948 examples, making those factory cars an enduringly collectible and unusual chapter in 911 history.

This new project also explains a small mystery that had caught enthusiasts’ attention last year. Porsche registered the “Flachbau” and “Flachbau RS” names with the European Patent Office in May 2025, setting off predictable speculation about a broader production model. The reality is more exclusive: the names were registered for this one customer-commissioned conversion of a 2018 911 GT2 RS with the Weissach Package.

A slantnose built for 2026

Porsche did not simply replace the headlights and call it a day. The front fenders were reshaped with slatted vents designed to evacuate pressure from the wheel arches, while the front bumper and fuel-filler arrangement had to be reworked to suit the new body contours.

The lighting is arguably the cleverest visual detail. In place of the 911’s signature round lamps sits a stacked LED arrangement with separate high-beam, low-beam, and daytime-running-light elements. Porsche says the high- and low-beam units are each just under four centimeters tall, while the daytime-running lights measure less than two centimeters in height.

It is a surprisingly modern answer to an old visual problem. The original slantnose Porsches used pop-up headlights to preserve the low fender line. This one uses ultra-slim LEDs to get the same effect without losing the technology, safety, or road legality expected of a modern performance car.

Grant Larson, the retired Porsche designer who also created Porsche’s modern 935 tribute unveiled in 2018, oversaw the design. That connection shows. The Flachbau RS is not a literal recreation of the 935/78, but it understands which details deserve to be carried forward: the flatter fenders, the compact lighting, the exaggerated rear aero, and the contrast-heavy motorsport color treatment.

The wing is not just theater

The most obvious clue that this is more than a styling exercise is out back. The Flachbau RS wears a new rear wing on distinctive S-shaped mounts, visually inspired by the wing fitted to the 992-generation 911 GT3 R rennsport. Porsche positioned it roughly five centimeters higher here and made it manually adjustable in three positions.

Depending on the setting, the rear axle generates two to three percent more downforce than a 911 GT2 RS equipped with the Manthey Kit in its comparable wing position. At 340km/h, in its High Downforce setting, Porsche says the Flachbau RS produces exactly 554 kilograms of rear-axle downforce.

Those numbers explain the broad package of aerodynamic changes. The car combines a revised front splitter with Manthey underbody components and a rear diffuser, while carbon-fiber rear-wheel aerodiscs help reduce drag. It is a very Porsche solution: celebrate the visual drama, but engineer the details until the drama earns its place.

Porsche and Manthey left the GT2 RS powertrain untouched, but the car still became lighter. Through extensive weight-saving work, the Flachbau RS sheds 31.6 kilograms compared with the already weight-focused GT2 RS Weissach Package.

That figure sounds modest until one considers the starting point. The GT2 RS with Weissach Package was never burdened with unnecessary luxuries, so removing another 31.6 kilograms required a fairly uncompromising approach.

A cabin with race-car priorities

The interior keeps the original mix of red Alcantara, black leather, and visible carbon fiber around the front seats. Behind them, however, Porsche has gone in a very different direction: less grand touring, more pit lane.

The Porsche Communication Management system is gone, replaced by a leather-trimmed storage compartment. The audio system has been removed, while much of the sound insulation and interior and luggage-compartment carpeting has been stripped away. Sections of bare, Grand Prix White-painted metal are left visible, and the simplified wiring harness is intentionally exposed beneath protective sheathing.

There is a certain honesty to it. Modern high-performance cars often lean on aggressive aesthetics while preserving every comfort feature possible. The Flachbau RS does the opposite. It accepts that a car built around lightweight construction, aerodynamic development, and track work does not need to pretend it is a relaxed daily driver.

Its small commemorative details reinforce the point. “Flachbau RS” is embroidered into the carbon-fiber bucket-seat headrests above a stylized Nürburgring Nordschleife outline, while the passenger-side dashboard carries a gold-colored Sonderwunsch badge engraved with “Factory One-Off 2026 | Flachbau RS.”

Tested like a production program

Perhaps the most impressive part of the story is that Porsche did not treat this as a display-only collector’s piece. Before the new panels and aerodynamic hardware entered production, the team carried out simplified crash simulations, airbag validation, structural analysis for the wing, and computational-fluid-dynamics work.

The wing itself endured vibration tests on a hydropulse rig and static load testing with sandbags. Porsche built three development vehicles for validation in lighting and wind tunnels, plus real-world road testing. The program included 50 laps of the Nürburgring Nordschleife and testing intended to simulate approximately 150,000 kilometers of customer use on the rear-wing structure.

That kind of process is what separates factory personalization from an aftermarket conversion, regardless of how talented the aftermarket builder might be. Porsche’s Sonderwunsch department has taken a client’s highly specific fantasy and subjected it to the same sort of discipline that governs a road car: lighting performance, aerodynamic balance, structural durability, and legal compliance.

The one-off also speaks to a larger truth about the modern collector-car market. Rarity alone is no longer enough. The most coveted cars increasingly combine a meaningful historical reference, a credible technical story, and an official link to the manufacturer. The Flachbau RS has all three, with the added advantage of beginning with one of the most formidable 911s Porsche has made.

Porsche has not disclosed a price, and it hardly needs to. This is not a car intended for a configurator or a dealership order sheet. It is a reminder of what can happen when a manufacturer with deep racing history, current engineering resources, and a willing customer decides that “special edition” is not special enough.