I'm running a Cobb catted DP mated to a stock STI catback. You're going to get most of your power gains just from the DP. You'll maybe give up ~5whp by sticking with the stock STI catback (don't know about the WRX cat back). I've been running my setup with a protune from EQ tuning for the last 3 years and I've been quite happy. I've never felt the car has lacked for power (for me).

 

Does the Cobb catted DP pass smog or do you revert back to stock dp when you need to smog it?

 

ah..I have no idea. We're military and my car is still registered in my home state so I haven't had to worry about smog. Also forgot to mention that my setup is quiet. Almost too quiet for some people. It sounds stock and I don't even hear it on the highway.

 

If you want to stay Cobb Stage 2 - you need an aftermarket DP - that's all there is to it.

Trust me on the Maddad turbo back - quiet and flow efficient, plus it looks stock...ish.

 

dp: gutted stock dp or Turbo xs stealthback.

axleback: stock, sti oem, or maddad