straight pipes do NOT always add hp. When i went from mufflers to just pipes on my mustang i lost 5hp and got 15ftlbs. Not saying your going to lose or gain anything. If you really want to see what its going to sound like just unbolt your cat from your down pipe and start it. If you do go straight pipe....you can always add muffler(s) later. But if i were you and if its your DD i wouldnt. not worth the little power you might get. get a nice magnaflow muffler and some 2.5 pipe, im sure your stock pipes arnt 2.5inch. Then you'll have a littler more power(maybe) but it will sound much better then just pipe. thats what i would do. Its your car though, do what you want and fuck the haters.