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^^^^I have a full PPE SetUp on my ISF. PPE Headers and PPE Dual Mode Exhaust. I have HiFlow cats in my system. IMHO, HiFlow cats are the right environmental thing to do. Also, some have mentioned a strong gasoline smell with no cats.
I have a friend with an ISF, PPE Headers, No Cats and a JoeZ exhaust. He has dynoed 6RWP more than me. He has no gasoline smell.