Are LS swaps legal in California?

Yes — if the swap meets the state's Engine Change Guidelines and passes a BAR Referee inspection. California (CARB + the Bureau of Automotive Repair) allows engine changes as long as they don't degrade the vehicle's emission controls. Anti-tampering law (Vehicle Code §27156, CCR Title 16 §3362.1) prohibits any change that does.

The core rules for every vehicle (Appendix D of BAR's Smog Check Reference Guide):

• Model year: the engine must be the same model year or newer than the vehicle it goes into.
• Same class: donor and recipient must be the same vehicle/engine classification by GVWR (passenger car, light-duty truck, etc.). A heavy-duty truck engine can't go into a light-duty truck even at the same displacement.
• Certification: California and Federal certification must match, or the engine must meet the stricter one — a California engine can go into a Federal vehicle, not the reverse. Bring proof of the donor engine's certification to the inspection.
• No uncertified engines: industrial/off-road engines and non-certified crate engines may not be installed in any emission-controlled vehicle. (A CARB-exempted engine package is the alternative — check its Executive Order for which vehicles it covers.)
• All emissions equipment from the donor: catalytic converters in the same position in the exhaust as on the donor (within 6 in for the close-coupled cat, 12 in for others), O2 sensors within 1 in of their original location, and only changes downstream of the last emissions device (e.g., muffler).
• Must pass the donor's tests: tailpipe test to the donor's model-year standards, OBD test for OBD II engines, working check-engine light, visual inspection of all emission controls, and functional tests.

OBD II matters: a 1996+ (gasoline) vehicle must receive an OBD II engine with the donor's full emission configuration, including the transmission, evap system, intake and exhaust. An older, pre-OBD II vehicle receiving an OBD II engine must keep the engine in stock certified configuration with full OBD II function; intake/exhaust changes are allowed only for packaging.

Inspection: every engine change must pass an initial inspection at a BAR Referee center and get a Referee label inside the engine compartment. After that, regular Smog Check stations can inspect it, and the smog check frequency doesn't change.

In practice for LS swaps: a junkyard LS from a newer vehicle, complete with its computer, sensors, cats and evap system, is the path that fits these rules. A carbureted LS or an uncertified crate engine in a smog-required vehicle is not.

This is a summary of the published guidelines, not legal advice. Read Appendix D in full and contact BAR before you buy parts.