No matter where it goes,it will be trying to enter a pipe already full.
..if anything logic would say it will create interference.Aside from that
the exhaust can't get out any easier or quicker?
The exhaust in the pipes isn't consistently "full". The exhaust is in pulses from each cylinder - "waves". So there are actual low and high pressure areas, but all moving pretty fast. The trick is to optimize the lengths and diameters of the headers, including and X or H additions in the system. Hold your hand to an exhaust pipe and you'll feel the pulses.
I put a 3" X-pipe and UltraFlo mufflers on my race car. It picked up between .05 and .10 over an open exhaust with collectors. I believe carb liked 1-2 numbers less jet as well after jetting was as good as I could get it with open headers. X pipe helped and those mufflers didn't hurt. I would think that 500+ HP would benefit more from a 3.5" exhaust.
