Originally Posted by m4a1mustang

Probably state safety inspection.

Here in VA we have an annual State inspection where they check to make sure your car is road worthy... so everything important has to work... like wipers, lights, horn, turn signals, windows, brakes, tires, etc. They usually take a look under the car for a visual inspection of the exhaust system.

I got burned once when the guy looked underneath my Mustang, saw my off-road X pipe, and said, "where are the cats?"

I wonder how they would react to HFCs, because it's obvious that HFCs are not stock as there is no heat shield around the cats like on the OEM parts. You aren't supposed to alter a properly functioning emissions system so technically they could fail you...