BMW built approximately 457 M1 super coupes. This production run lasted from 1978 up through 1981, during which time BMW teamed up with Lamborghini to deliver its wedge-shaped machine as a homologation special. To press more cars into the hands of buyers, BMW created the M1 Procar Championship. This one-make racing series ran for two years and drew participation from some colossal names from the racing world.

Today, the M1 Procar racers appear at a handful of high-level vintage racing events. Such was the case recently at Spa-Francorchamps, where three of the cars were set loose. 

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The sound you're hearing comes courtesy of a road-racing variant of a remarkable street car. The M1 Procar racers are a bit different in a number of ways compared to the road cars--most notable is the fact that their M88 straight-6 engines make 470 horsepower compared to the 273 horses of the road cars. The cars also have adjustable anti-roll bars, adjustable brake bias, and race-ready steering racks.

We don't think the road car ever spit this much hot fire, either. The tail area of these M1s are running rather hot as they rip and roars through the famed Belgian circuit. It's an amazing sight to behold, but it also means a lot of unburnt fuel is finding its way through the engines. It looks cool, but it's not efficient.

Still, we'll take cool over efficient when it comes to a car like the BMW M1 Procar.

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