X pipe H pipe or side by side

chrispy1971gtx said

I talked to a gentleman on here who runs a Pure Stock Drags 340 GTS and he claims .3 tenths improvement on an X-pipe 2.5" exhaust alone.

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That is intresting but also raises a few more questions.
Is that gain from replacing a restrictive stock exhaust?
And is parts of that gain from the X helping those poor manifolds do partialy what a set of headers could have done for the same engine?