How best to make 25 extra horses out of a grand am gt?

I am trying to get a grand am gt that has a pounds to horsepower ratio of 17.5 down to 15. that would require 25 extra ponies. does anyone know of the best way to do that, without cutting corners through NOS, messing with the IAT sensor, etc. i have heard that while the exhaust from the cat and on is pretty good, the exhaust manifold is pretty restrictive, but there arent any headers for sale outside of a expensive custom set... is this true? oh, and when it makes the 25 extra horses, would the tranny be able to hold them? if it helps, the engine is a 175 horse 3400 series v6 (idk what the cam situation is though). thanks for the help!