The addition of an X or H pipe has more of an effect on a V-8 configuration, performance wise but it helps the inlines. It will cut the acceleration and cruise decibals down big time (took my cruise exhaust sound back to stock), as compared to a simillar exhaust without the X pipe (or H), definitely make it more mellow/deeper. I would use an X or H pipe as an aid to achieve a certian tone with the inline, than for a performance purpose.
