Found a lot of threads close to this subject but didn't want to hyjack them. I'm definitely going to buy the Pacesetter headers for my 00 SS but i'm thinking of putting cats on this time. How badly do the cats hurt hp gains from headers?

 

High flow cats are generally a total of 10hp loss. To keep the drone and loudness down I think it's worth it.

 

319rwhp, is that on the normal for a A4 LS1 with headers?

 

Depends on the cats.
I've seen dyno comparisons where the difference was a mere 2 hp.

 

No there was a little tuning done there as well.

 

2-5rwhp difference