Actually... the "emissions" equipment on cars only does one thing... it takes the pollution that cars made in the 70s and turns it into another form of pollution... it just hasn't caught up to us yet... it isn't like they can take car exhaust, run it through a cat and have it breathable.
And if you drive in the midwest, you can see when you are approaching a large city by the orange "bubble" of pollution encircling it... so much for "emissions" control on new cars.
And, if you do some reading and some research, you will find guys that took a late 60s car (I believe a 396SS Chevelle?) running high octane fuel (like that of the time) and had less emissions than a 1984 buick skylark with a emissioned-to-death 4 cylinder... and getting better fuel mileage to boot... plus they had power. My buddy has a 1968 Chrysler New Yorker with the only-option 440 4bbl and gets 25 mpg on the highway... 5000 pounds of car, no lockup converter, no OD, NO EMISSIONS CONTROL EQUIPMENT...
To me, fuel in equals exhaust out... it is a direct relation... the better fuel mileage a car gets, the less exhaust (and therefore emissions) it will expel.
In reality, the cars need the fancy high-tech emissions control to clean up the exhaust because of THE FUEL we are forced to run through them... again, we are getting the shaft from the oil companies. Regenerated fuel?? Oxygenated gasoline??? Not existing in the 1960s/70s.
steved