As far as I have been told, headers are a PITA to deal with on mod motors, and unless the engine has been at least moderately modded, the gains are minimal...
H-pipe or x-pipe is your choice.
The gains are similar:
with the x giving you a slight edge in the top end and the h giving you a slight edge in low end torque...
The sound of the system will be the biggest noticable difference. Listen to both setups and pick the one you like best!
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"The Yellowjacket"
Ricer 1: What the heck was that!?
Ricer 2: I don't know. It looked kind of like a yellow SN95 Mustang.
Ricer 1: Nah, fast SN95 Mustangs don't exist... Must have been a mirage or something...