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That being said, you can get headers with hi flow cats. A good tune and the car will pass the sniffer. Some smog places only check to see if the cats are in place and don't look to closely at the headers. The question is do you want to take the chance?
They must be CARB approved to be legal. That said I must say I had CARB approved headers on my motorhome and for approximately 5 smog test I was never ask about them.