What does California's smog referee require for an LS or Hemi engine swap in a Jeep, and can it pass the sniffer anyway?

California allows engine swaps that meet its Engine Change Guidelines (BAR + CARB). An LS or Hemi in a Jeep can pass — if the swap is done the way the rules require. The key rules:

• Model year: the engine must be the same year or newer than the Jeep.
• Same vehicle class: donor and Jeep must match classification by GVWR (for example, light-duty truck to light-duty truck).
• Certification: California-certified engines can go in Federal vehicles, not the reverse; bring proof of the donor engine's certification.
• All the donor's emissions equipment, with catalytic converters in the donor's positions (within 6 in for close-coupled cats, 12 in for others) and O2 sensors within 1 in of original placement.
• OBD II: a 1996+ Jeep must receive an OBD II engine in the donor's full emissions configuration, including transmission, evap system, intake and exhaust.
• No uncertified crate engines in an emissions-controlled vehicle.

The "sniffer": yes — the Referee runs the tailpipe test using the donor vehicle's smog requirements and standards for its model year, plus the OBD test, a working check-engine light, a visual check of all emission controls and functional tests. After passing, the Jeep gets a BAR Referee label and future smog checks can be done at regular stations.

Full summary: are LS swaps legal in California?. Not legal advice — check with BAR before you buy parts.