h-pipe size

[dbusch]

what is the proper h-pipe size for a 4" exhaust? this is on a drag car with a relatively short exhaust system. I was thinking 3.5" h-pipe but a 3" would be easier to fit...

[LilRacr]

Why not go with a full size X pipe?
I have never seen any results in the flow of an H pipe, but some have seen real world gains with the X pipe.
Of course it could be the systems I have played with, i have not done one over 3", but plan to do one soon with a 3 1/2" on my car.