Any modification beyond stock from the intake to the catalytic converter has to be approved by the California Air Resources Board(CARB) to be legal. While most CAI and SR tubes are nearly identical, this process is used by the state of CA to A) Promote a standard of quality and not limit pollution and B) To provide funding for pollution related programs (Getting a CARB number is an expensive process costing in the tens of thousands, I heard).

When a piece proves to not excessively impact emissions, it's grated a CARB E.O. number, which states that the Cali ARB has decided this is an OK modification.

A complete listing is available here: http://www.arb.ca.gov/msprog/aftermk...es/devices.htm

Let's see who can spot the Environmental Studies major