Thinking of exhaust mod

H-pipe exhaust systems balance the pressure between the banks, X-pipe systems do more by pulling the gases on each pulse of exhaust.

There is quite a bit of info on the subject...here is a quick Google Search Result from the popular Car Craft Exhaust System Comparo:
http://www.carcraft.com/techarticles/exhaust_system_installation/index.html

Enjoy, good luck!