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Old 05-17-2009, 05:28 PM   #3
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Originally Posted by RaceFaceXC View Post
You could use any cat with the appropriate ID, 2.25" being the accepted best compromise for good velocity and high flow volume on a non built EJ253. But if you have stock header still then there is a cat in there so replacing the second cat would be to very little gain. It would also require custom bending because no one makes a bolt up catpipe for the 06+ impreza. If you have already changed headers then this would not be a concern.
Ahh, I thought the cats were on the same pipe, my mistake. My searching wasn't good enough. I'll get a look in under my car when I rotate my tires Friday, but all those stupid heat guards under there make it impossible to get an idea of where stuff is at, and i don't have a lift to just pull stuff off easily

I would search for more info on this because I think the stock cat(s) is not a restriction unless you have significantly increased the flow rate of the engine via cams, etc. I could be thinking of the muffler, though.
When I gutted my muffler I posted on the forums here and everyone said it was basically pointless to gut it without replacing the cats in front of it. I'm doing this to free up some efficiency, hp is just a side effect to me

Also, magnaflow and dynomax make generic HFC's that you could fab up a piece with, too. I'm sure there are more companies too
Ya, I did some initial research and Vibrant claims CFM of up to 578, but I think that is for their more expensive race HFC. I want to have something around 500 CFM or more.
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