Tunes, Intakes and Turbos: Street Legal in California?

What the law prohibits

Vehicle Code 27156 works on two levels. A vehicle that is required to have pollution controls may not be driven or left standing on a highway unless those controls are correctly installed and working, and no one may disconnect, modify or alter them. Separately, no one may install, sell, offer or advertise a device that alters the original design or performance of a required pollution control system. The exception is a modification the Air Resources Board has found doesn't reduce the effectiveness of the controls, or keeps the vehicle within the emission standards for its model year.

Two exhaust rules sit beside it. Every registered vehicle with an engine needs an adequate muffler and no cutout or bypass (section 27150). And no one may modify an exhaust to make it louder than allowed; for vehicles under 6,000 pounds GVWR other than motorcycles, a sound level of 95 dBA or less, tested to the current SAE standard, complies (section 27151).

How the exemption works

CARB calls its exemption an Executive Order. A part receives one after a CARB engineering evaluation, and it applies to the specific emission-controlled vehicles it lists, not to every car the part happens to fit. Each exempted part has an assigned number that a Smog Check station, a BAR referee station or CARB can verify, and CARB publishes a lookup tool for checking parts before you buy them.

Parts that commonly raise the question

• Engine tunes and software flashes.
• Cold-air intakes and throttle bodies.
• Headers and exhaust components ahead of or around the catalytic converter.
• Turbocharger and supercharger kits.
• Anything marketed "for off-road use only" or "for racing only".

That last label is a warning, not a loophole, for a car you drive on public roads.

The insurance side

California lets insurers rate on vehicle performance and on characteristics such as damageability and repairability. A tune or forced induction changes the car your policy was priced for, so declare it. Added parts are commonly limited unless listed, and a car that won't pass smog can also run into registration trouble, which brings its own insurance headaches. How an insurer views modifications that aren't street legal varies, and a claim is the worst time to find out.

Buying a car that's already modified

A modified car comes with its modifications' legal status. Before you buy, ask for the parts list, receipts and Executive Order numbers, and consider having a Smog Check or a shop look at it first. A part with no exemption is now your problem to reverse, and an emissions failure can hold up registration renewal. Price the car as if you might have to return it to stock.

Before you modify

1. Look up the part and your exact vehicle in CARB's database and note the Executive Order number.
2. Keep the part's documentation and the installer's invoice with the number on it.
3. Ask your insurer how the change affects the policy and how the part is covered.
4. Expect your next Smog Check to look at it.

What varies by insurance company

Appetite for modified cars, how performance changes are rated, custom equipment limits, and the documentation required all differ between insurers. An agent who can compare several companies is useful here.

Modified already? Quote the car as it really is and list the parts.