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Aftermarket Performance Parts

Installing Aftermarket Parts: I want to install some aftermarket performance parts on my car's engine but I'm worried I might have a problem passing the CA smog check. I want to install a turbo unit, air intake unit, and exhaust headers. How can I find out if the upgrade parts I want to use are California smog legal, and won't fail the emissions test? What about OEM parts?

What You Must Have: Engine performance upgrade components such as upgrade ECU, turbo units, exhaust headers, intake manifolds, and other emissions related components can pose smog check problems, however if proof is shown that the upgrade units are legal for use in California (they posses an EO number) or they are OEM parts, they will not cause a vehicle to fail the California smog check.

EO stands for Executive Order. This is a number given to the emission upgrade component by the California Air Resources Board (CARB). The EO number indicates the performance upgrade part is California emissions legal.

Most manufactures of aftermarket performance parts will stamp the EO number on the unit or they will print in the unit's manual or other document which pertains directly to the performance upgrade component being installed or inspected.

Most late model upgrade components however will have the EO number stamped on the upgrade parts body.

You must present this number to the smog station where your vehicle will be getting a smog check in order to pass the visual portion of the smog inspection.

Which Parts Are Smog Legal? Aftermarket engine upgrade components sold at local California automotive part stores are CARB approved and posses EO numbers. Buying an upgrade component locally in California is a safe method of performing engine upgrades.

Performance upgrade components bought online or out-of-state might require a little bit of leg work to ensure they will not cause a California smog check failure.

A non-emission related component does not need an EO number. A typically non-emission related upgrade component is the air filter unit.

Air filter units which do not have any sensors on them and allow for the proper connection of all existing air intake hoses and vacuum lines are not considered emission components in most cases.

EO Number Search Tool: Use the following link to lookup current California Air Resources Board approved aftermarket engine upgrade parts. EO Number Search Tool

If the performance upgrade component which you want to add or install on your vehicle, whether it be a supercharger, turbo unit, air intake, headers, ect. is not listed on CARB's website, it is not for legal use in California, except for off-road use only in certain circumstances, and it might cause your vehicle to fail the smog inspection.

What are OEM Parts? OEM is an acronym for Original Equipment Manufacturer.

Which Type Should I Choose?


Manufacturers often produce components that are purchased by a company and retailed under the purchasing company's name. When referring to automotive performance or upgrade parts, OEM designates a replacement component made by the manufacturer of the original component.

Installing OEM parts often protect a vehicle's warranty and will ensure your vehicle does not fail the smog check for an emissions system tamper. Using OEM parts is always recommended.

Will aftermarket headers cause my car to fail the smog test?

Unless the aftermarket headers you purchase and install have an EO stamp, meaning they have been tested by the California Air Resource Board and been issued an Executive Order number, yes they will fail the smog inspection; as a tampered emission component. Exhaust headers, not to mention the entire AIR Air injection system is an "emissions component". Any modification to the headers, intake manifold, or exhaust manifold, including removal of a "Y" tube from the exhaust pipes (if equipped) is considered an emissions tamper. Your vehicle will fail the smog inspection even before the tailpipe exhaust is checked.

Mufflers: The smog test does not test the muffler. However we don't recommend you take the vehicle in for testing if your vehicle's muffler is broken or has holes in it from damage or rust. It may cause the smog technician problems getting the smog machine to accept testing your vehicle.

Smog machines are calibrated in California every three days, and are designed to not allow the testing of vehicles which emit oxygen levels exceeding a smog machines preset limits. In other words, if your vehicle's muffler has large holes which are allowing oxygen to be vacuumed in with the emissions stream, the test results would have been inaccurate. The smog machine may not allow the inspection to continue and/or fail the smog inspection.

Aftermarket emission regulations apply to all vehicles being operated on California public roadways, including the following manufacturer brands - Acura, Alfa Romeo, Aston Martin, Audi, BMW, Bentley, Buick, Cadillac, Chevrolet, Chrysler, Lamborghini, Daihatsu, Dodge, Eagle, Ferrari, Ford, GMC, Geo, Honda, Hummer, Hyundai, Infiniti, International, Isuzu, Jaguar, Jeep, Kia, Daewoo, Land Rover, Lexus, Lincoln, Lotus, Maserati, Maybach, Mazda, Mercedes Benz, Mercury, Mini, Mitsubishi, Morgan, Nissan, Oldsmobile, Peugeot, Plymouth, Pontiac, Porsche, Rolls-Royce, Saab, Saturn, Scion, Smart, Sterling, Subaru, Suzuki, Toyota, Volkswagen, VW, Volvo.