BMW made an M5 wagon with a McLaren F1 engine

The M5 wagon was used as a testbed for the F1's V12.

The BMW E34 M5 Touring was the super wagon of its day. With over 300 horsepower from its straight-six engine, the M5 wagon was the ultimate go-fast grocery getter. Or was it?

As it turns out, BMW one-upped the factory-built E34 M5 Touring with something rather more special. In the Collecting Cars podcast hosted by Top Gear's Chris Harris, David Clark -- the man in charge of McLaren race and road cars between 1994 and 1998 -- revealed that BMW built a one-off M5 wagon prototype with the 6.1L V12 engine that would be later used by the mighty McLaren F1.

BMW used the V12-powered M5 wagon -- which Clark says remains in BMW's possession to this very day -- as a testbed for the McLaren's 627-horsepower engine. The experiment obviously worked, with the F1 going on to become one of the most legendary cars ever built.

Moreover, Clark says he's actually driven the M5 Touring prototype. And judging by his description, the drive was just as good as you'd imagine. "I've driven, it's an outrageous thing,” he said.

It remains unknown where BMW has kept the F1-engined M5 wagon squirreled away for all these years, but hopefully Clark's story will prompt BMW to bring it out of hiding for all to see.