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The metallic substrate cats are the least resrictive. And unfortunately the most expensive. An alternative would be a set of a Dynatech Headers metal cats which are available from JEGs or SUMMIT for about $149
Wish I could help you, Robert, but I don't recall which RT bullet cats I have installed. At any rate they're the round ones and I tend to think they were the metal substrate jobs. I have them installed behind my headers with stainless steel band clamps. I had two lengths of straight pipe cut to fit in their place for racing, but to be honest, I've never bothered with swapping them.
The metallic substrate cats are the least resrictive. And unfortunately the most expensive. An alternative would be a set of a Dynatech Headers metal cats which are available from JEGs or SUMMIT for about $149
The Metal Matrix flow better. On a stock engine it probably wont make much of a difference, but on your modified engine it does.