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General Smog Check

Engine Change Guidelines in California

In general can I legally replace the engine in my vehicle with any other engine I choose, whether it be a larger engine, older or newer, or different number of cylinders... like a 6 cyl to an 8?


When rebuilding an engine, it must be rebuilt to the original equipment specifications. However, if you decide to change an engine (install an engine not originally designed for your vehicle), the guidelines below must be observed to ensure that the vehicle will pass a smog inspection and subsequently be eligible for California registration.

Remember, these are guidelines for performing engine changes -- not certification procedures. All exhaust emission controlled vehicles with engine changes must be inspected by an official California smog check referee station and must have a Bureau of Automotive Repair (BAR) Vehicle Identification Label affixed to the doorpost (or chassis).

Remember also, state and federal anti-tampering laws generally prohibit any modification to the vehicle's original emission control system configuration as certified by the manufacturer. And, Section 3362.1 of the California Code of Regulations prohibits any engine change that degrades the effectiveness of a vehicle's emission control system.

California Engine Change Guidelines

- California Certification A federal Environmental Protection Agency (EPA) certified (federal or 49-state) engine cannot be used in a vehicle that was originally certified for California.

- Certification Standards.  Make sure the engine and emission control configuration on exhaust - controlled vehicles are certified to the year of the vehicle or newer, and to the same or a more stringent new vehicle certification standard.

- Classification.  Don't mix engine and vehicle classifications which will degrade the emissions certification standards. For example, a heavy-duty engine cannot be installed in a light-duty exhaust-controlled chassis even if they have the same displacement. Non-emissions controlled power plants such as industrial or off-road-use-only engines may not be placed in any exhaust-controlled vehicle.

- Computer Controls.  If a computer-controlled engine is installed in a non-computerized vehicle, the "CHECK ENGINE" light, the Original Equipment Manufacturer (OEM) diagnostic link, and all sensors, switches, and wiring harnesses needed to make the system fully functional must also be installed.

- Emission Control Configuration.  Mixing and matching emission control system components could cause problems and is generally not allowed. Engine and emission control systems must be in an engine-chassis configuration certified by the California Air Resources Board (ARB) or U.S. Environmental Protection Agency (EPA). The engine must meet or exceed the requirements for the year and class of vehicle in which it is installed.

- Emission Warranty.  Voiding the vehicle manufacturer's emission warranty is not allowed.

- Engine Modifications.  No internal or external engine modifications (cams, pistons, intakes, etc.) may be performed unless the parts are ARB-exempted or EPA-certified for use in the installed engine. Use the database on this site to search for aftermarket parts covered by ARB Executive Orders.

- Original Equipment.  The installed engine and host chassis must retain all of their original emission control equipment. Diesel-to-gasoline conversions must have all gasoline engine and chassis emission control systems installed (such as fill pipe restrictor, catalytic converter and evaporative emission system).

- Smog Inspection.  These vehicles must pass a complete smog inspection (visual, functional, and tailpipe).

This information is directly from the BAR. We posted this because of how stringent they are on engine changes. It is difficult for us to determine legal engine changes. Only a smog check referee can make the ultimate decision on whether or not a vehicle has had a legal engine change.

IMPORTANT NOTE: After the swap is complete, the vehicle will have to be inspected by a California State Referee. The Referee will ensure that the job was done properly and that the new engine does not pollute. If the vehicle pass the referee's smog inspection, the referee will issue you a BAR label which will be placed on your vehicles chassis and will be an indication that the vehicle is California emissions legal.

We highly recommend speaking directly with a State Smog Referee before beginning any work. You can contact the referee by calling (800)622-7733.

posted by SmogTips Support

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