I remember when I lived in California and I took my car, fresh from Wisconsin, into a smog station. I had a 64 LeSabre with the little 300 engine. They retro fitted out of state cars with what was nothing more than removing the vacuum advance hose and plugging the fittings at the carb and distributor. They set the advance to a pre determined level and that was it. Simple? Not if you drove a lot of highway miles. Anything over 55 mph was gonna burn your valves. Most of us "in the know" would just re install the vacuum line and tune the advance back to factory settings. It was just California's way of getting rid of older cars through attrition of engines going bad and the car really not being worth much to begin with and just junking it and buying another California car with it's required smog equipment that the 49 state cars didn't have at the time.
That move was another Jerry Brown special ! That idiot made the B.A.R. add a NoX Sensor to cars which were not originally equipped with such a device ; my dad's 1969 Dart got nailled with that piece of junk NoX Sensor . Basically , it retarded the timing via the distributor vacuum advance ; a real MPG killer !!!
Circa 1984 : The year we were finally freed from the talons of Brown : My dad receives a letter in the mail stating to the effect , "The NoX Device is no longer necessary on your [1969 Dodge] ..." So , as quickly as he read the letter , he was out under the hood of the Dart , removing that piece of junk sensor ... ha ha ha ... I can still see him throwing it as hard as he could , bouncing-off the pavement as it were , throwing a bit of a spark as its metal body spanked the asphalt .
I must admit that I'm surprised that a 1964 model year car had to meet Ca's restrictive standards ! For many years , only 1966 & newer cars were subject to the probing of the B.A.R. creeps , with one exception : engine swaps !
For many years , the vehicles were expected to meet the emissions standards of the year of the car's engine !!
So , a handful of sharp fellers were swapping older engines into their newer cars , thusly avoiding smog tests !!
Witness the then-common practise of swapping a Buick 215 V8 into Vega and LUV trucks ; a CCV (predecessor the the PCV) was the only piece of smog equipment on those engines (and , an improvement to the lifespan of the engines vs. Road Draft Tubes !!) .
Beginning in c.1984 , the smog testing guidelines changed ; now only 1966 & newer cars were subject (why 1966 ? First year for A.I.R. Pump ... though not every engine was so equipped) , regardless of the year of the engine under the bonnet .
As I've said time and again : I like clean air . I do not miss the days of 3rd & 4th Stage Smog Alerts . But , I also realise that there's a point of 'diminshing returns' when it comes to emissions inspections . It's just not realistic to make every vehicle subject to fuel-mileage-killing catalytic converters / restrictive exhaust / electronic carburetors / etc. !
It's been proven twice that modified engines can and do produce less harmful emissions ; however , new(er) cars with their superior fuel injection / dry induction (especially Direct-Injection setups !) , conversely , run worse when their equipment is fiddlled with (read : fart cannon exhaust crowd).
Too much money to be made by running at the pipe testing ( no visual ) , and excepting vehicles 20 years old and older .