I have a stock 455 with a 650 holley carb, and was wondering what some basic mods would be that I can do myself to gain some extra HP. The engine currently has 180 hrs from 1974, and has never been rebuilt. The boat is a 21' day cruiser with a Berkley pump, not sure of the impeller cut. Im currently spinning 4300 RPM's, and only seeing a speed of about 40-43mph. Eventually I would like to put a BBC in, but for now I'm gonna wait until this one explodes!