I was helping a friend change out his exhaust and he purchased a new stainless steel headers wit what he was told are high flow cats. When I look down the pipe I see a hollow tube. The part that supposedly has the cat in it has a thicker wall with perforations in it but I can stick my arm down the pipe with no obstructions. I remember seeing the inside of my cat when it was replaced and there was a honeycomb like material in it with tiny holes lined up parallel to the air flow.

Is what my friend has a high flow cat? I don't see how this can work as most of the exhaust passing through the pipe will not come into contact with any surface area so how does it break down the pollutants in the exhaust?

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