It must pass tail-pipe emissions, a dyno test (in Smog Check II areas like the LA basin), and pass a visual inspection. The latter is what demands factory-correct pollution control devices.
Example: Someone in Sacramento (SCII area) has an '86 Chrysler wit the Mitsu 2.6 motor. It fails the test - as most of those motor do. One cause is the distributor. The law states it must be factory. But, those are no longer available. So, the owner swaps in a 2.2 Chrysler motor form the same year, with all of the controls in place and operating. Result? FAIL!! It MUST be factory!!!
That's a true story. About twenty years ago you could buy a Dodge 400 or a Chrysler Le Baron for about 200 bucks if it had the Mitsu motor - they will not pass and you cannot change them except for what the VIN dictates what was in the car. It's crap!!
