Do a search on this topic it has been talked about many times. The H gives you a louder muscle car type of sound while the X gives you a exotic sound.
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347 W/ A-trim 6#'s, Canfield heads, out of the box Victor 5.0 intake, solid roller cam. 11.1 @123mph 1.46 60FT
93lx 5.0 daily driver
MY CAR
http://www.mustangworks.com/cgi-bin/...splay.cgi?1288