A 553-horsepower, 4.4-liter Twin-Power Turbo V8 shared with the X5 M and X6 M behemoths, plus the small matter of 500 pound-feet of torque between 1,500 and 5,750 rpm. Redline is now right around 7,200 rpm instead of the discontinued E60 M5's V10 that smacked us around at 8,250.
Source: http://www.autoblog.com/