In Mustang land, that is called an H-pipe. The ideal is an X-pipe that is two bends siamesed in the middle for very smooth flow. The H-pipe makes more power than a dual exhaust with no connections (and the x-pipe makes the most of all). The purpose is to equalize exhaust pulses.
I don't ever remember seeing a test with either design on an exhaust system that converges into one, with the exhaust with no connection of the secondaries. It may have gained a little bit, but I think that it supports the header as a primary purpose in life. Maybe it kills a little noise, with out affecting exhaust flow at all??? Thats a nice benifit. On Mustangs, the pipes have a smoother sound. They seem to be a bit quieter, and have less tones that will make your ears bleed. Probably due to the exhaust pulses being split. On the MRT exhaust, the pipe meets again, but the pulse has to travel farther through the H-pipe, so it takes longer to travel to where the pipes converge, taking a different time to get there, it has an opertunity to blend with another pressure wave creating a pressure wave that was simular to the one that left the cylinders. Effectivly doing nothing but taking longer to do it. Or the pulses could fall between each other in the pipe. How much this changes with RPM, I don't know. MRT may not either, they may have just put it on and got lucky.
16 HP is pretty good. Better than the Borla, but it is a superior design already, and that is for the complete system, the borla probably had to be tested with the stock cat. We all know that a good cat back is worth a good chunk of HP as well. Knowing all of that, the H-pipe design of the MRT probably doesn't hurt it, but it doesn't make a significant ammount of HP either.
ION performance is suposed to do a header shoot out between Brullen, Borla, and MRT. We will have answers then. (If ion does an honest job at it, and not use the stock cat and muffler with the Borla, or a straight pipe for an exhaust on the brullen. They have an interest in seeing Brullen win.)
EDIT: This is all assuming that the tube is indeed a pathway. You could call MRT and ask, I think they would tell you straight, there would be no reason not to answer you , or tell a lie. There isn't much of a way to tell if you don't have access to one of those little cameras on a long stiff wire, other than drilling a hole in the cross piece near the joint and seeing if you can feel the wall of the other pipe in the place where the hole should be.
Greg
