| It depends, it is regional. You need to check with your specific location if they have smog laws. It must be approved in order to be put on your car. Engine swaps are legal, but the engine cannot be older than the car you are putting it in. Example, if I have a 2002 honda civic I cannot swap a 2000 Honda civic SI engine into my car. For the most part, if your car doesnt make strange smells or isent really loud, or doesnt have obvious violations, like blue and red lights flashing like a police signal. You shouldnt have a problem. Nitrous cannot be used legally at all on the street, and if you have a burst of speed and an officer sees it, they can check your car for nitrous.
Diemos | 
