I just installed a borla header on my stock exhaust system. I have to say driving it was the most anti climatic thing i have ever done. Acceleration didnt improve, and the tone didnt change much. I was quite dissapointed. My question is, at this point, is it the cat section of the rest of the exhaust system that is choking it, the muffler section, or the genral small tube size.
I am going to be piecing together my own system and i want to get the most restrictive portion replaced first.

 

Headers on a stock exhaust won't yield much in terms of power or sound. The mufflers obviously have the biggest impact on the sound (pipe diameter and to some extent the cats have a smaller impact), and remember that if your exhaust has to travel through a 1.75" (2"?) section of pipes after the headers, that's still going to cause your exhaust flow to be restricted even if you have headers.

 

I understand that. What i am asking is what yealds the biggest flow improvement replacement of the cat section to one that is catless or replacement of the muffler section. I dont care about tone all that i ask is that it is quiet enough to pass by a cop at half throttel without getting an unnessasery noise violation.

 

Replace the cat-back section with a 2.25" exhaust. 2.5" is too big, I know from experience. stock is much smaller.

 

Cat back is what you need now, and usually that's how you build a Subay NA exhaust, from the back forward. When you mate the catback with the header is it of much better sound and performance. Then the last straw will be the high flow cat section and that is where you gain the loudness and more performance. And stick with 2.25" as stated above. Brian

 

Hey u guys help me a lot. I should start from the muffler section and work my way up cool. I got a question, is it true Borla Hearders aren't compatible with Auto trannies?? I got a 2003 Forester same motor as the RS.

 

some one installed it on an auto car and had issues with the tranny lines to the radiator. I guess they rubbed agenst the header and melted.
https://www.i-club.com/forums/engine-power-non-turbo-all-non-turbo-imprezas-61/stupid-borla-header-103565/
other than that i haven't seen any thing to make me think they arent compatible.