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Old 05-17-2009, 05:10 PM   #2
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Join Date: Dec 2007
Chapter/Region: South East
Location: Central Floriderp

Originally Posted by ScubaruImpreza05 View Post
It's that time of season again, the mod bug is attacking I do a little bit of modding every summer, and this summer I'm thinking of doing something about my restrictive catpipe and getting some struts. I already have STi springs and I opened the muffler and gutted it last summer, as well as made Williaty's intake and new plugs

Anyways, to start off, are the only 2 companies making high flow cats Stromung and Random Tech? If so, is Random tech really worth the extra $200 premium over Stromung?

Also, would it be difficult to make your own catpipe assuming you had these tools at your disposal: Mandril bender, Welder and appropriate piping? There is an exhaust shop not 4 minutes from my house, but I'm cheap and the old man has an industrial welder and access to a mandril bender. If I got my hands on an appropriate High Flow Cat, think I could mod me up a custom cat? Or is it a bad idea?

As for the high flow cat, if I got one that was correct diameter and made for....let's say a 200 HP car in stock trim, would that suffice? I'm going off of the thought 'More HP means more air' so the flow would be good I assume?

Thanks for any ideas
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.

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.

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
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