04 gto have the 5.7 liter v8 ls1 engine. SSingle side dual exhaust that looks lame as well as a normal hood that's boring. 05-06 gtos have the 6.0 liter v8 ls2 and has split dual exhaust which looks sweet as well as hood scoops and all around better gto. (IMO) ls1 cranks about 350hp and 360 trq while the ls2 is 400 hp/trq