Using the 15-percent rule, the 2013 M5 would lay down 476 hp at the wheels. The idea of BMW underrating its engine outputs is nothing new. Earlier this year, the new 328i show some impressive ...

Based on the M49 motorsport engine used elsewhere in BMW's motorsport division, the M88 gave the subtle looking M5 saloon 278bhp, more than a contemporary Ferrari 328 at the time. The M5 was ...