As so well explained by both Jerry and Roger an H or preferably X pipe will both show an improvement in performance. Generally speaking however, that performance improvement is relatively minor and probably not enough to even be noticed in most driving situations (especially with a street driven motor under 300 cubic inches). The biggest difference you will likely see will be in the exhaust tone.

The one thing I would suggest if you use an H or X pipe is when you have your exhaust built is to pay close attention to the routing of the pipes. Often times if a transmission needs to be pulled or in some instances even a starter removed it may be necessary to drop the pipes. This can be a big PIA on a custom system made system where all the joints have been welded. If I’m running an H or X pipe, I often use a pair of ball and socket joints just before the mufflers so the whole pipe can be unbolted and removed for maintenance if needed.





Just my 2 cents.



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