Technically, It is a federal offense to tamper with or render inoperative the emissions components on a car in any state. But the feds are few and far between and largely leave it up to the states to regulate and enforce the laws to suit their own objectives.
Speaking of federal laws that are still on the books, did you know it is a federal offense to have flame throwers on your exhaust system? The law dates back to prohibition era. They were considered evasion devices.
Of course it is also against the law to exceed the speed limit - but sometimes I do 56 in a 55 MPH speed zone.
