This mad BMW M5 has a VW W10 engine and was owned by Ferdinand Piech

Funny, huh? Back when the E39 BMW M5 was busy conquering everything in its path, Volkswagen was apparently determined to build a rival super saloon using an experimental W10 engine. But it didn’t have anything to slot it in to test.

So under the direction of the late Ferdinand Piëch – architect of the Bugatti Veyron, among many, many other things – a W10 was stuffed under the nose of… the all-conquering E39 BMW M5.

This is that very car. The same W10-engined E39 M5 prototype owned and driven by the late Dr Piëch. Now, it’s coming up for sale.

Like the BMW’s 5.0-litre V8 it replaced – replaced! – the W10 is also a naturally-aspirated 5.0-litre lump, producing 473bhp and 437lb ft, matched to a six-speed manual driving the rear wheels. That’s significantly more than BMW M managed with its own S62 (394bhp/369lb ft).

The resulting performance, according to Broad Arrow Auctions, filled the M5’s gorgeous, timeless lines with “a more immediate, unfiltered character behind the wheel than any factory M5 offered”. Big claim, that. Apparently the traction control, stability control and ABS systems were all deactivated.

It’s a fascinating prototype, used and driven in secret by a fascinating character. Apparently, the project was never an official VW thing, more something Piëch simply asked for at a cost reportedly totalling €2m. He drove it himself, too, and we’re told that while it’s a prototype, it’s a properly driveable thing.

It keeps the BMW interior equipment mostly intact barring the aftermarket dash with no odometer, so nobody has any idea how many miles it’s done. The current owner bought the car about a decade ago, drives it regularly (bravo), and serviced it back in 2025.

Broad Arrow Auctions reckons it’ll go for anywhere between £215k and £300k (€250k-€350k) at next week's Belgian sale. Possibly more, if you consider that, according to one of the engineers behind the project (Sabine Willeke) only three of these W10 engines were built.

One remains in Germany, one’s bolted inside this M5, while the third will be offered alongside this lot as a display. What a thing.

Photography: Broad Arrow Auctions