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People always talk about doing exhaust work for sound, and sometimes I hear people talk about exhaust work for performance. What I'm wondering is I always hear the terms cat-back, which I understand means having work done from the catalytic converter back. My concern is that your performance wouldn't really be improved unless you did the full exhaust system. Am I correct? The previous owner of my car put a "performance muffler" on my car, which makes it sound really dumb, in my opinion. Not having done the rest of the exhaust, he literally changed ONLY the sound, correct? I guess my main question is, will I notice a difference in performance if I go stock exhaust? Also, what difference will I notice in performance and gas mileage if I upgrade the rest of the exhaust instead?

 
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From the cat-back, you won't notice any significant gains but it will let your exhaust flow a bit easier. If you want to actually start gaining power form exhaust, you'll have to replace the whole thing, header-back. The catalytic converter and downpipe are the most restrictive parts of the system. You can buy a high-flow cat or eliminate it altogether if you don't mind burning the ozone layer And the downpipe is basically a tube filled with coffee straws so it's not very efficient. Replacing these should give you a bigger perfomrance gain, but overall you won'tget much unless you're running a forced induciton system.

 
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what krud said ^ also look into a cheap ebay intake and throw a k&N filter on there you'll see gains there too

 
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Right, but again, minimal gains. It's mostly for sound and better breathing for your engine. You'd have to put a lot of money into an exhaust system if you want more power.

 
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I actually already have a K&N short ram intake, which I was also wondering about. I just don't appreciate when cars make loud sounds if they don't have any real power, so I was considering going stock on all my parts.

 
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i noticed some gains but i guess they were minimal in the long run and on top of money a fully redone exhaust is illegal because the cat is typically deleted or replaced with a test pipe so you wont pass inspection unless you swap back to stock headers literally every inspection. youd probably confuse your ecu somewhat too when doing that but thats just an assumption of mine

 
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Cool. Thanks for the help guys! Now I feel better deciding to go all stock.