Think 10-cylinder BMW 5-Series, and undoubtedly, the first car to pop into your mind would be the E60-generation M5. But apparently, there’s an earlier 10-cylinder 5er out in the world, and the reason for its existence could be the key to remembering a long-forgotten engine that never got past the prototyping stage.
Indeed, it appears a Volkswagen W10-engined E39 BMW M5 is out there. A car that still exists, and worked well enough back then that it was pressed into daily service by VW’s CEO.
Not only could it be one of the few instances of cross-pollination between BMW and VW — as off the books as it may likely have been — but it also serves as a reminder that there are still some untold skunkworks prototypes that are still being uncovered decades later.
Related: McLaren Tested The F1’s BMW-Developed, 6.1-Liter V12 In An M5 Touring
Volkswagen has been known for its unconventional “W” engines, with the W8, W12, and W16 units, the latter being the staple of Bugatti. But there was another “W” creation that never quite saw the light of day — at least in a production capacity. That was the W10.
While the W12 engine was created by mating two VR6 engines to each other, the W10 was conceived as a smaller alternative utilizing — yes, you’ve guessed it — two VR5 engines spliced together. The VR5 was a shortlived offering only available in a handful of Volkswagen products and markets, but it offered a creditable-for-the-time 168 hp and 162 lb-ft of torque for its 2.3-liter displacement.
Had the W10 made it into production, it would almost certainly have found life in the heart of the VW Phaeton, which instead made do with V8 and W12 engines. But the W10 was never officially announced — so then, how did one end up in a BMW M5?
It turns out that Ferdinand Piëch, Chairman and CEO of VW at the time (and devout fan of the W engine), commissioned the rule-breaking engine swap. The E39 M5 chassis was chosen as Volkswagen didn’t have anything comparable to be used as a test bed. Allegedly, Piëch liked the mule so much that he used the newly W10’d M5 as his personal vehicle.
More: Take An In-Depth Tour Of The Canceled VW Phaeton Successor
The car is now on sale, offered by Belgian-German GT racing team GDM Motors. The car is listed as having 500 hp (507 PS / 373 kW) and 550 Nm (405 lb-ft) of torque. That’s a 25 percent bump in power over the standard E39 M5 with 10 percent more torque.
The engine bay looks immaculate, with hoses, wires, and fuel lines all neatly tucked away, adding credence to the claim that this was far more than just a shoehorned homebrew special. With an engine like a W10, which was never officially a thing, the chances that this was indeed Volkswagen’s test bed makes a lot of sense.
Of course, none of this has actually been verified by Volkswagen, and we wouldn’t hold our breath on it either. But mixed-auto-race test mules are far from unheard of. It also wouldn’t be the first time a BMW M5 was used as the basis for prototyping a hairy-chested engine either: in 2019 it was revealed that McLaren shoehorned the BMW-built 6.1-liter V12 destined for the F1 into an E34 M5 Touring for testing.
