im gonna be looking into buying a complete itr exhaust (cat back)for my ls is there a header that thats a perfect combo for it and will i have to swap the cat in my ls for the itr cat or will it bolt right up to the ls cat...what gains (if any )can i expect with this setup...thanks

 

it will bolt right up, no neede to get a new cat. however most people consider getting a high flow cat since the stock cat acts as a major bottle neck in the exhaust system.
dunno bout which header, im looking around to general opnion is that unless your willing to spend big bucks the dc 4-2-1 will be fine. id like to get the comptech 4-21 but its a bit too much money