[geaux_tigerss]

I put 2" TSP headers no cats to my factory NPP catback. With the NPP valves closed it isn't much louder than stock. NPP valves open..... wake the dead.

Before I did headers I had pulled the fuse on my NPP. Occasionally I would wake the wife and kids in the morning when I left for work. After headers I put the fuse back in and have been starting it in stealth mode. I haven't woken anyone since then.

So I guess to summarize, headers with NPP valves closed is quieter than factory manifolds with NPP valves open.