The Y pipe and downtube? I already have an SLP "SS" muffler off a friends 02 35th SS. How much HP would I gain from headers and and a new exhuast system?
Wes
Mods: K&N filters, SLP Muffler, Sony Xplod headunit, and some kind of aftermarket speakers (haven't looked yet).

 

the y-pipe is really bad. its kinda of to tell in the pic but gives you a idea.

<img src=http://content.communities.msn.com/_Secure/0MQBlO8cQGJAnALb6ZfHZ69QWFTw*eRlNY37j8NHPkdZTTI95FJfjBPiCBF7aElDXq84BI0*!OvmBLAxPXcmBtg/Image025.jpg>

 

Like said the stock manifolds and y-pipe are really restrictive. And should be among the first mods done, to allow any other mod to meet its potential. I would say headers with a y-pipe are good for 15-20hp and with a cat-back, perhaps another 10hp.