Legally, according to FEDERAL law, ALL of the original emissions equipment must stay on the car and be functional, regardless of where in the United States you live.
That said, in a city/county/state that doesn't inspect, you can get away with almost anything, but it doesn't make it legal.
Even in states with inspections, there's loopholes. In Texas, for instance, my '75 Mustang II would still fail a visual for not having an EGR valve, PCV valve, AIR pump, factory-style air cleaner with pre-heater tube, and the charcoal canister (which is there, but not connected). It would pass in spite of no longer having catalytic converters because Texas doesn't require them on cars built before 1984. None of this directly matters because the car doesn't get inspected because it has Antique plates which exempt it from inspection and a front license plate. All of it is still technically illegal.
Bench racing aside, we are one election away from having nation wide emission standards testing in all cars in all states. Better save everything you take off if you do not want your car impounded.
The EPA started a royal crackdown on performance parts under the current administration, threatening to even go so far as to start sending agents to dirt tracks and drag strips. This is currently being battled in the courts, not the ballot box.
I seriously doubt that. The politicians can't even get the manufacturers to stop lying about car emissions, which is of far greater concern than dynoing the 1% of cars on the road that aren't OBD2. There are far better ways to curb emissions than to build thousands of test dynos.
Kurt
There are better ways to reduce emissions at the tailpipe than farm subsidies for ethanol to be added to gasoline too, but that's still happening because it garners votes. If the politicians think dyno manufacturers will give campaign donations and hire the right lobbyists and PR people to make the idea popular, it'll happen.
