Mmmmm, I had 370bhp on a T4 with Greys.......with all the right ancillaries, standard cams and head. Not my favorite though, but that was just me, and a T4 which didn't seem as responsive as others that Karl has done. To get a genuine 400bhp on a standard engine you need to use alot of boost 2bar at least, so you really need a very good head gasket, and a strong low milage engine............In my opinion.

370BHP Ish would be more likely, and that's enough for most.