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Old 04-08-2020, 11:41 AM   #1
mjm4jc
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Default Exhaust manifold/header compatibility

Hello everyone,

I have a 2009 NA sedan pretty much stock. As you know, the exhaust manifold is actually a header with the CAT built into it. I noticed that on the previous generation Impreza, the manifold is basically a manifold and not a header. It also does not have the CAT built into it. My question is if someone had a bad CAT in the 09 header and had a spare 02-07 manifold, would there be a problem with putting the 02-07 manifold in it's place and then using a high-flow CAT to continue the exhaust?

I look forward to your comments.
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Old 04-11-2020, 08:28 PM   #2
Boxcar80
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That should not be an issue as long as you keep the O2 sensors before and aft of the converter. But please be aware that some high flow cats are not as efficient as the stock ones and my trip a P0420 code.
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Old 04-11-2020, 09:30 PM   #3
mjm4jc
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Thanks for the reply. The difference in the headers seems to be that the 08-14 are 4 individual pipes that convert into 1, whereas the older generation are 2 pipes on each side that convert into one. I'm not sure if this will have any difference in power or sound. If I decide to go this route, I'm assuming that I will have to extend the O2 sensor harness?
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Old 04-12-2020, 08:01 PM   #4
Boxcar80
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Quote:
Originally Posted by mjm4jc View Post
If I decide to go this route, I'm assuming that I will have to extend the O2 sensor harness?
Yes you will. The first O2 measures the exhaust so the computer can adjust the injectors for proper AF mixture. The second O2 checks the efficiency of the cat.
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Old 04-14-2020, 08:43 AM   #5
Lilyjess18
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Pretty sure the two dump on different sides of engine. Might have some hack and weld.
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