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Catalytic converter advice needed

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So I searched but can't find a clear answer: What are the most effective and durable catalytic converters for a dual duty street/track day car? 2011 GT, totally stock motor and tune. I want to stay emissions legal which requires cats here in MA. I am struggling with 0420/0430 codes after the original cats failed at about 140K miles. I tried aftermarket Walker cats but they failed pretty quickly. I am looking for no code and durable, and I suppose a better flowing cat would be a nice benefit if possible but not really a priority. Is a 200 cell sport cat such as the Magnaflow likely to throw a CEL? Would it hold up better than a 400 cell oem cat? Should I just go back to oem Ford?

I just posted a wanted classified for oem Ford cats but I'm not sure if that is the best approach?

Sorry for all the questions. Any advice is much appreciated, this is frustrating.
 
Stock part numbers for a manual transmission 2011 5.0 are BR3Z-5E212-B & BR3Z-5E213-B if you don't find any low-mile take offs. I'd be with TMSBOSS in that a 140K service interval is pretty good for anything in a performance environment. If the original catalytic converters had melted or you had plans in doing a fire-breathing engine upgrade, then the extra expense and fabrication on something like a GESI catalytic converter would make sense. Cell count alone doesn't necessarily dictate total flow as the length of the internal cell substrate also plays a role, so if you do go aftermarket just keep that in mind when talking with the manufacturers.
 
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Mad Hatter

Gotta go Faster
5,204
4,186
Santiago, Chile
I had the Kooks hi flow cats... they couldn't take the heat and ceramics became unattached to the canister after two seasons.
 
1,068
1,057
Exp. Type
HPDE
Exp. Level
5-10 Years
Lenoir City TN
I had the Kooks hi flow cats... they couldn't take the heat and ceramics became unattached to the canister after two seasons.
Did you have the regular Kook's high flow cats or their Green Cats? I have been looking at them and understand the Green Cats are more heat tolerant, but you pay for that.
 

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