Before the mighty 6.1-liter V-12 developed for the McLaren F1 made its way to the supercar, it was proven in a peculiar prototype vehicle: a BMW E34 M5 wagon.

BMW built and tested a one-off M5 wagon prototype with the 6.1-liter V-12, and BMW still has the car, too. The Collecting Cars podcast, which "Top Gear" presenter Chris Harris hosts, spoke with David Clark last month, who was director of McLaren road and race cars from 1994-1998. He revealed the story of the BMW M5 wagon as the test vehicle for the massive V-12 and said he's also driven the car.

1998 McLaren F1 LM-Spec for sale

"It's an outrageous thing," Clark said of the V-12-powered M5 wagon. We can only imagine, but a 627 horsepower M5 wagon with 479 pound-feet of torque sounds marvelous. Although those aren't gobsmaking numbers by today's standards, recall that the M5 made 311 hp at the time and 266 lb-ft of torque.

Clark added the M5 wagon prototype still resides at BMW as part of a secret collection of prototypes. However, the public has never seen the car. Perhaps with Clark's comments out in the open, BMW will be more open about showing the incredible car off.

1998 McLaren F1 LM-Spec for sale

Although Clark has nothing but love for the 6.1-liter V-12 and the F1 itself, the program, he said, was not a cash cow. In fact, he was ordered to find a way out of the engine deal with BMW after the F1's launch. BMW was supposed to supply 350 engines, but McLaren only built 106 cars.

Today, there's nothing quite like the F1, but that will soon change. Gordon Murray, the instrumental design figure behind the F1, plans to introduce a successor the beloved supercar. The supercar will house a V-12 and even a manual transmission. Murray said the car is the last chance for companies to build something in the spirit of the original F1 as emissions and regulations start to squeeze more traditional supercars out of production.