its quite simple. find out where your nearest Brabus dealer is and tell him how much much horse power you want, and he'll put it in there for you o(at a cost of course with this kind of quality)
my father owns a BRABUS tuned 5.0 v8 2001 s500 and it rapes anything that comes near it. i havent been allowed to drive it due to my inexperience.
it contains a factory brabus stroker kit(stroked to 5.8 i think(?) and brabus exhaust and extractor system and supercharger. can you say ferrari killer???