[quaddriver]

yes - TEL was phased out for new cars, with no legal means for anti knock, it required a compression de-tune as well as ignition retarding and some other crap.

plus the insurance industry became weenies.

1975 was the monolithic converter for HC emissions for MOST cars, some other cars with smaller engines using lean burn or stratified charge methods were able to do without (the lowly chevette and many hondas come to mind)