Thats bogus as hell. Theres no way they got 400HP outa a stock 5.0 with only a head, intake, carb, roller coversion. My 85gt has a roller 5.0HO and its stock puttin out 210hp. The intake might give ya 20 hp., the carb a few more, and the heads (Ive read between 30-60 hp.). Even at its best...