The easiest to engine to get to mega hp levels is the Cosmo 13bre/20bre engines if you only want 450fly hp then any of the FD twinturbo 13brew engines will get you there with single turbo and porting. They are basicly the same engine but the Cosmo version has larger diameter runners so breathes that bit better. You also have the option of the 20b three rotor but your talking lots of £ for this option. Hp wise with a 20b it\'ll do about 300hp N/A before you start adding turbo\'s then the sky\'s the limit 500/600hp on stock ports and about 1bar of boost. With porting and more boost?
Hope this helps.