Apparently, according to this video from Summit Racing, the X Pipe will always make more horsepower.
I decided to look this up because my brother put an X Pipe onto his gorgeous 2005 Mustang GT and the sound and fury kind of blew me away. He disliked the rather exotic sound and swapped it for an H Pipe about a week later and the results were a quieter exhaust under 2500rpm and less exotic, more hotrod sound. I like both but must admit that I favour the exotic sound of the X Pipe while Trevor favours the hotrod sound of the H Pipe. He did note, though, that he lost some “punch” when he installed the H Pipe, which is confirmed in the video above.
For those who want to hear the actual difference, you are in luck. I filmed a ride in the car with both the X Pipe and the H Pipe and the differences are very audible. The X Pipe occupies about the first 2/3 of the following video with the H Pipe finishing it off.
I had not even heard of such technology before we did the filming … I must admit that I am intrigued. Gotta get me one of those :-)