BMW has revealed the M2 with M xDrive, a new all-wheel-drive variant of the compact sports car.The twin-turbo inline-six now sends its 473 horsepower to all four wheels, but the all-wheel-drive system retains a rearward bias.BMW says the M2 with M xDrive will hit 60 mph in 3.3 seconds, three-tenths quicker than the rear-wheel-drive M2.