A rare prototype BMW M5 with a secret Volkswagen W10 engine is set to go under the hammer at Broad Arrow Auctions on October 9, 2026. The vehicle, estimated to fetch between €250,000 and €350,000 (approximately $285,000 to $400,000), is the only road-going car ever fitted with this engine, a sign of its unique engineering heritage.
The auction will take place at the Zoute Concours in Knokke-Heist, Belgium. This unique M5, built in 1999, features a naturally aspirated, all-aluminum 5.0-liter W10 engine producing 473 hp and 437 lb-ft of torque, a direct precursor to the quad-turbo W16 that later powered the Bugatti Veyron.
A Secretive Swap Ordered by Ferdinand Piëch
The story behind this prototype begins with Ferdinand Piëch, Volkswagen’s chairman at the time. In 1999, he directed his engineers to develop a W10 engine for a high-performance sedan, aiming to rival the BMW M5. Piëch, who had taken over Volkswagen in 1993 when the company was on the brink of bankruptcy, was known for his engineering-first approach, which he instilled across the brand. Instead of creating a new test vehicle, the team installed the engine into an existing E39 M5 chassis dated March 2, 1999.
The car retained its six-speed manual gearbox and was finished in Carbon Black Metallic with a black leather interior. Chassis WBSDE91040GJ16436 appears indistinguishable from any other M5 on the outside. Modifications included disabling traction and stability control, anti-lock brakes, and installing a stand-alone ECU to manage the engine, reflecting the car’s experimental nature.
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Engineering Detours and Unique Features
The M5’s instrument cluster was replaced with an aftermarket Stack racing dash lacking an odometer, making its mileage unverifiable. The current owner, who purchased the car about a decade ago through engineering contacts, has driven it regularly, though it still lacks a certificate of conformity. This detail shows the car’s status as a one-off prototype rather than a production vehicle.
The W10 engine delivers 79 hp and 68 lb-ft more than the original S62 V8. Its ten cylinders and single crankshaft provide exceptional smoothness, while the stand-alone electronics offer sharper throttle response. Only three W10 engines were ever produced, according to Sabine Willeke, who led the engineering team. One remains in Germany, another is displayed alongside the M5, and the third powers this unique car. The project, costing nearly €2 million ($2.3 million), was built outside Volkswagen’s formal R&D structure and served as Piëch’s personal transport during development.
Impact on the Collector Car Market
More interesting cars for sale include a screen-used 1992 Batmobile expected to fetch $7 million, the first Ford Bronco Raptor No. 00001 with only 99 miles, Steve McQueen’s Ferrari NART Spider headed for a $20 million auction, and Monaco’s first supercar targeting $1.29 million at auction.