Before the current BMW M8, the automaker toyed with building an M version of the wedge-shaped E31 8-Series of the 1990s, even building a one-off prototype. That car recently resurfaced in a video from BMW Group Classic, including interviews with some of the engineers who developed it.

The E31 M8 prototype has a version of the S70 6.0-liter V-12 used in the then-new 850i coupe. This engine developed 550 hp, and was fed by a massive intake duct designed to keep incoming air as cool as possible. It also needed additional throttle valves to lower idle speed, which would have been 2,000 rpm to 3,000 rpm without them, an engineer said. It was a real bear to get this car to drive slowly.

In the interest of keeping weight back and low, the car also has a dry-sump lubrication system, with the oil reservoir in the trunk because there wasn't enough room under the hood. Oil is fed to the engine through lines in the roof, and the flow can be heard from inside the car, one the engineers said.

BMW M8 (E31) prototype

BMW M8 (E31) prototype

While BMW chose not to build the M8, it green lighted the tamer 850CSi, with a 5.6-liter V-12 making 375 hp. A production M8 wouldn't arrive until the current G15-generation 8-Series. Available as a coupe, convertible, or four-door Gran Coupe, the G15 M8 uses the S63 4.4-liter twin-turbo V-8, which makes 617 hp in Competition models.

The prototype M8's V-12 didn't go to waste, though. A version of it was later used in the McLaren F1, and yet another evolution was used in the Le Mans-winning BMW V12 LMR prototype racer. BMW even stuffed the Le Mans-spec V-12 into an X5 SUV.

The original M8 prototype was thought to have been destroyed, but was revealed to still be in existence in 2010, and was subsequently restored by BMW. After sitting for three decades, the lining of the racing-style fuel cell had disintegrated, but the car is now in running condition. Check out the video to hear it fire up and learn more about the car. Perhaps we'll see it in motion in a future video.