x and y pipes
they're all different beasts... an X oR H will yield more power... and sound better IMO
the difference between X and H is mostly sound and extremely small power gain for the X
the H will have more of an old school muscle sound to it and tends to make a stock motor sound cammed
the X will still have an excellent rumble ( I'm biased all tthe cars ive worked with had X's or lanes duals) and have more of an exotic sound up top..
but the Y pipe is easier if you absolutley have to run the exhaust out the back but dont have access or the ability to get true duals fabbed up.
Theres a million threads on this.. just search and peruse the threads.

