If you live in california and are planning on doing a motor swap but wondering about smog problems, check this out this is what i found straight from the California Air Recorses Board web site Replacement Engines Entire engines can be replacement parts. As with any other replacement part, the engine must be identical to the original. If the replacement block or engine is obtained without emissions equipment, all the equipment from the original engine must be installed on the replacement block. If the engine is not identical to the original then it is not a replacement part, instead it is considered an engine change. Engine changes are a modification that must meet certain requirements to be legal (please see "Engine Changes"). Japanese Replacement Engines Used engines imported from Japan can be used as replacement engines as long as the engine being used has been identified as functionally identical to the original engine. Please refer to the engine importers catalogue to determine if a replacement engine is legal for installation in your vehicle. Engine Changes Engine changes are legal as long as the following requirements are met to ensure that the change does not increase pollution from the vehicle: The engine must be the same year or newer than the vehicle. The engine must be from the same type of vehicle (passenger car, light-duty truck, heavy- duty truck, etc.) based on gross vehicle weight. If the vehicle is a California certified vehicle then the engine must also be a California certified engine. All emissions control equipment must remain on the installed engine. After an engine change, vehicles must first be inspected by a state referee station. The vehicle will be inspected to ensure that all the equipment required is in place, and vehicle will be emissions tested subject to the specifications of the installed engine.