i own a 2002 v-6 mustang coup bought it new i guess its 3.8 it has power but...

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...i had mach 1 351? and my question is how and what would i do to step up the horse power with out getting to expensive i have kn air filter its automatic shouls i apply duel exaust and what else shall i do silver fast back 2002 3.8 v6 bought it new it has power but i want the rumble power with least expensive cost i heard about a chip also that can be purchased