Is it illegal to add a catalytic converter?
So searched the forums, couldn't find anything on adding a catalytic converter.
My question has multiple parts:
1) is it illegal to add a catalytic converter?
2) also does positioning matter, say adding one cat before first O2 sensor in addition to the factory one which comes between O2 sensors.
3) this kinda is the same as second part, adding multiple cat in replacement of one cat. For example, turbo'd a car, but wanted to stay environmentally friendly, (lets not worry about performance/back pressure issues as this is just me stating an example), and i added 2 cats in the place where there were one factory to help minimize emissions released into the air, is this illegal?