I've track tested a 5.7L with an X and an H, there was absolutely no difference in times. This was tested on a Naturally Aspirated 5.7L that ran slicks and very consistent 9.2 sec.
1/8 mile we have no 1/4 mile in SoCal.
It was 9.2 sec. either way and that was his brick wall, so he installed a turbo. :lol5:
but in the mean time, I can say that running true duals on a stock manifold, stock catted truck will lose a lot of low end torque.
The pic above with the AeroTurbine exhaust looks great!! That works real well on a stock manifold truck.
Here's how I set em up with a muffler that releases it's backpressure right at your engines peak volumetric efficiency:
Untitled by
bamufflers, on Flickr