This could get debated till we're all blue in the face. But I will say from my experience, when we changed the H pipe to an X pipe on my sister's Mustang years ago, the car pulled harder in the top end and sounded better in the top end as well. I think that the H pipe sounds better than the X at idle and lower rpm though. I've always seen that the X usually comes out a little ahead in power overall over the H when tested side by side. But that may also depend on what the combination is. Here's the X on my car with UltraFlo's
