What engine modifications can be done while still allowing the car to pass the California smog test? Intake? Turbo- or supercharging? Exhaust? What are those of you in California who are making modifications that won't pass smog planning to do when your next smog inspection is due?

Everything from intake to cat is covered by CARB and requires an EO (executive order) exemption to replace with a non-OEM component. Cat-back exhausts are unrestricted.

Strictly speaking an aftermarket part may pass smog emissions and still fail the smog check simply because it's an aftermarket part w/o a CARB EO number.
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Recall Nexium (http://www.classactionsettlements.org/lawsuit/nexium/)

Funny you should ask... Racing Beat sent out their news letter about the new intake. It had a link to their Emissions FAQ (http://www.racingbeat.com/emissions.htm).