yes headers do add power between 5 to 10hp, by letting the motor breath easier, anything that restrict's the flow ( like catytlic converter) reduce's horsepower, i picked my headers up for $85 bucks off ebay from a ebay store so u can still find them there, as far as the demon coil goes, u'll find it's double the spark power than standard ( add's up to 5hp)and u can find that for under a $100 bucks also. i bought my diablo tuner on ebay for $150 bucks ( used) are you gonna beat a hopped up gt? hell no and that's not really the point here u will shock a stock gt though when u get the jump on him but sound like a v8 lol