If you consider yourself to be a hardcore BMW fan, chances are you might have heard about the company’s one and only E31 M8 prototype.

BMW Group Classic has restored the historic prototype, bringing it back into working order and promising that everyone will see it roar once the weather conditions allow it. The biggest challenge was the replacement of the racing fuel tank, which is made out of rubber with an inner lining of foam that had disintegrated as time passed by.

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The one-off E31 M8 was a skunkworks project created by a handful of BMW M engineers in the early 1990s with the goal of creating a genuine supercar killer.

When the first prototype was completed, the management simply pulled the plug on the whole project, deeming it too expensive for production. BMW never even showed the prototype, keeping it locked and hidden away from the world’s eyes for the best part of 20 years.

They finally revealed the one-off E31 M8 in 2010, surprising everyone and spreading warm fuzzy feelings to fans. It looks just the right amount of purposeful, with its excellent box flares, the subtly more aggressive bumpers, and the side air vents, reminding everyone of an era when cars didn’t have to scream at you with their design.

Under the bonnet lies a unique V12 engine with dual overhead camshafts, measuring 6.0 liters in capacity and with an astonishing output of up to 640 HP – in 1990! This sort of power was simply unheard of at the time, with the most powerful 8-Series then being the 850CSi, which offered 380 HP.

The engineers mounted the engine as far back and low in the chassis they could for the best weight balance possible. For that reason, it also features dry-sump lubrication, with the oil reservoir mounted in the luggage space and the oil lines running through the roof because there wasn’t enough space in the engine bay.

“Whenever oil is being fed back and forth, you can hear it moving through the lines in the roof”, said one of the original engineers that worked on the M8 Prototype.