What makes a Catalytic Converter illegal in California?

-What is it that makes it illegal here in this Liberal state. I want to buy Magnaflow high flow cat, but california is the only state that doens't let you buy one. Any help please?In california any aftermarket part that is not to OEM Spec must get tested by and approved by the California Air Resource Board. And will have a CARB # that you need to display under your hood so smog techs don't fail you on visual. Its not that it is illegal, just not approved. It is an expensive process and one most aftermarket parts makers choose to bypass.



One way to get around it is to find another car that has a stock higher flowing cat (most sports cars) order one of those, and adapt it to yours. It will look OEM and no tech should be able to tell.