That's the BMW international site. They base hp on kw. Conversion of 300 kw = 407 hp for the 550. Maybe the U.S. rounds it to nearest 100th so 400hp. That same site states the 535 has 306 hp while US specs it at 300 hp. Difference is so minimal. It's just how a particular region wants to market it. Maybe someone more technical on engine specs can chip in their 2 cents.
2013 BMW X5 35i
Alpine White | Cinnamon Brown | M Sport
2013 BMW 550i
Titanium Silver | Black | M Sport
Last edited by Decboy; 01-29-2013 at 11:35 AM.