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I don't claim to be an expert but in talking to my tuner last this subject came up during our conversation. We were talking about FI motors, specifically the LS3, and how durable they have been. He told me they only recently had a supercharged LS3 come back in with problems with the #6 cylinder. When they got into it they found customers cats caused the issue. Customer was running 'hi-flow' cats with a supercharger. What happened and is occurring with other FI cars running cats is the supercharger/turbo is pushing so much exhaust that the bottleneck becomes the cats. This is causing the cats to heat up more than on a NA motor. The substrate inside the cats is expanding so much due to the heat that it is breaking down and then getting pushed, or in at least one case that my tuner saw - spun/twisted, into the cat and tries to actually push the material out of the cats. As you can imagine the material then clogs up the HI-FLOW cats causing all the heat to back up into the cylinders/motor causing some bad mojo to occur. My tuner is of the opinion that if you are running a FI setup that you need to remove the cats. His opinion of HI-FLOW cats is that they don't flow as well as the manufacturers claim. That being said, they will work fine on a NA engine, but definitely not built for FI applications. Fortunately I live in a state where they don't 'sniff' test. I just have a slip piece in my exhaust in case I would ever have to put the cats back on for any reason. I have a set of brand new HI-FLOW cats in the garage but don't plan on using them unless I would sell the car.
Like I stated earlier, I'm not an expert on this but just relaying what I learned last week. It makes sense to me that if the cat material is breaking down and plugging up then the heat absolutely has no where to go but back into the engine. I talked to Shardik2ss about this. He has a Whipple and its running so hot it burned his hood liner!! He is running cats and is supposed to get them checked. I'm waiting to see what he finds out as well.
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