first off im a newbie but im not really familiar with searching here but i have a 04 silverado w/ the 4.8, cold air intake, no cats, and i was wondering if i was to go true duals will it hurt my performance, also wat sizze pieing do i need to run

 

if you want to go duals, don't go any larger than 2.25" piping. The cross sectional area of that is slightly larger than a single 3" which is what a lot of folks run. The smaller pipe will help keep exhaust gas velocities up in the lower rpm, which in turn helps cylinder filling, which in turn helps low-end performance.

 

i think you would see better #s with a y set up with a 4.8, but as pathfinder said if you decide to go with duals stay close to 2'' tubing

 

no need for duals on a 4.8, low end already sucks as it is. the stock 2.75 is more than enough to handle anything you throw at the motor.