Enforcement of the previous law and regulations in California, for example, resulted in many drivers being pulled over by state and local police and cited for improper modified exhaust systems despite having what they believed to be legal aftermarket exhausts. To prove our a point (and educate itself ourselves) about the widespread improper enforcement of the previous California exhaust law, SEMA conducted a series of exhaust noise tests in early April of 2001. First, we contacted California SEMA Action Network members to see how many folks had received citations for excessive or modified exhaust. We were surprised and dismayed to learn how many fit the category. We (SEMA) then invited them to have their cars tested to see if they actually complied with California law. Finally, we hired a board-certified acoustical engineer to do and did the testing according to the standards set out in California law. Long story short, of the cars we tested only one exceeded the 95db legal level.
To remedy this problem, in 2002 SEMA helped enact a new enforcement procedure in California through its model bill. The new law forces compliance with an objectively measured standard in a fair and predictable test. Through this procedure, motorists who drive vehicles legally equipped with modified exhaust systems can confirm that they comply with California's exhaust noise standard. The California Bureau of Automotive Repair began operation of the motor vehicle exhaust noise-testing program in 2003. The law also allows courts to dismiss citations for exhaust systems that have been tested and for which a certificate of compliance has been issued. Under the program, the 40 Smog Check stations statewide that provide referee functions are performing the test. These referee stations are issuing certificates of compliance for vehicles when tests of their exhaust systems demonstrate that they emit no more than 95-decibels, under the SAE test procedure.
Hobbyists frequently ask about the rules governing engine switching in project vehicles. First of all, those engaged in engine switching activities are bound by specific state laws that may vary from state to state. Your State may make you jump through hoops, though. Take California, which has its own unique engine-switching laws. The Bureau of Automotive Repair's (BAR) website stipulates that any engine switching must not change or degrade the effectiveness of a vehicle's emission control system, and that the engine and emission control configuration on exhaust-controlled vehicles must be certified to the year of the vehicle or newer, meeting the same or more stringent new vehicle certification standards.
Having said that, there are some general guidelines one may consider. This pertains to the rules for switching the engine in production-type vehicles (but not specially constructed vehicles, street rods, kit cars and the like). The basic rule of engine switching (as opposed to installing a "replacement" engine) is that the change must do no harm. This means that the engine being installed must theoretically be at least as "clean" as the one taken out. Several requirements may define "clean" for the purposes of engine switching:
Model Year: The engine to be installed must be the same age or newer than the one being replaced. Crate engines can be used if they are configured to resemble an engine that was certified by the U.S. Environmental Protection Agency and/or the California Air Resources Board. This essentially means that the required emissions parts must be present on the engine.
Certification Level: The engine to be installed must come from a vehicle certified to meet the same or more stringent emissions standards than the one replaced.
Vehicle Class: An engine from a vehicle class such as a motor home, medium-duty truck or marine application must not be used since these engines were certified to different types of emissions standards, using different tests.