Automakers may have started the horsepower wars decades ago but tuners are even more determined to squeeze every last drop of performance from sports cars. This BMW M4 Coupe already makes over 500 horsepower in Competition guise when it leaves the factory, and yet the owner wanted to push the inline-six’s output into supercar territory.

It might look like a fairly standard G82 from the outside but the secret is underneath the hood where the twin-turbo 3.0-liter engine has gone through a stage 3 upgrade. Equipped with a pair of custom turbos from Dutch aftermarket specialist Mosselman, this S58 engine now pumps out a ludicrous 830 hp while torque has been lifted to a mountain-moving 915 Newton-meters (675 pound-feet).

You’d think this kind of power makes some sense on an xDrive-equipped M4 but this sports coupe is rear-wheel drive. Suffice it to say, it’s a real hoot to have this much power going exclusively to the rear wheels as long as you know what you’re doing since being overly enthusiastic with the accelerator pedal could rapidly turn into a disaster.

The amped-up M4 Competition Coupe was pushed hard on an unrestricted section of the Autobahn where it delivered some neck-snapping acceleration. It needed a little over five seconds to go from 62 to 124 mph (100 to 200 km/h) and posted a sub-five-second time for the 124 to 155 mph (200 to 250 km/h) sprint.

Flat out, it effortlessly reached speeds of up to 186 mph (300 km/h) and the eight-speed ZF automatic transmission doesn’t seem to have a problem with having to handle this much torque. With xDrive being able to better put all that power down, this upgraded G82 would be even quicker, but even so, it’s an absolute rocket.

This must be one of the fastest street-legal cars out there with a six-cylinder engine, and we’re particularly fond of how the owner decided not to modify the appearance. To some degree, this is a sleeper.

Source: AutoTopNL / YouTube