Broad Arrow will auction an unusual E39 BMW M5 that served as a Volkswagen development car around the turn of the millennium. Instead of the standard BMW V8, it carries an experimental naturally aspirated 5.0-litre W10 commissioned by Ferdinand Piëch, then head of the Volkswagen Group. Broad Arrow says Piëch personally used the car during the testing programme.
The auction house quotes 473 hp and 592 Nm, paired with a six-speed manual gearbox. Only three prototype W10 engines are said to have been built. One remains in Germany, a second will be included with the auction lot on a display stand, and the third is installed in the M5.
Broad Arrow presents the programme as part of Volkswagen's wider experiments with W-layout engines that later produced W8, W12 and W16 production units. Classic Motorsports describes the car in the same broader development context. The exact technical lineage should not be simplified into a claim that every later W engine was a direct derivative of this particular unit, but the prototype clearly belongs to the Piëch-era programme that pushed Volkswagen toward unconventional multi-cylinder layouts.
The car is scheduled for Broad Arrow's Zoute Concours Auction on 9 October 2026 in Knokke-Heist, Belgium, with an estimate of €250,000-€350,000. Its collector appeal is rooted less in conventional rarity than in provenance: it is a one-off E39 M5 carrying an experimental Volkswagen engine and associated directly with one of the most influential automotive executives and engineers of the period.
Many development mules disappear once their programmes end. A surviving, running prototype that combines two rival German brands and documents a little-known branch of Volkswagen's engine research is a much rarer proposition.