Originally Posted by GT500MUSTANGFAN View Post
Better gains with the back-pressure offered by the X-pipe, ideal for those running without Cats. However the H-pipe offers better/equalized flow, as long as the mid-connector pipe is open.
Actually, it's the other way around.
The reason that the X does a better job of equalizing flow is because the crossover paths are far 'gentler' in the X and offer less restriction to the crossing flows. This is most important during those brief periods when you've got two cylinders in the same bank firing in sequence and that side's pipe sees a peak total flow that's maybe 25% higher than either cylinder's own peak flow.
The difference isn't huge, but it's there. And FWIW, an X manages to eke out a little more power than an H or straight duals when you're stuck with relatively restrictive mufflers.
'08 GT coupe, 5M, wheels, tires, pads, fluid, a few suspension mods . . . still almost stock height
'19 WRX, 6M (the "family sedan")
'01 Maxima 20AE, 5M (the spare and occasional winter driver)