the gas crisis of the 70's ended fast cars, for a long time, and emissions f'ed us too. and it stopped auto racing for a while too.
the late 60's was the real end of big bad muscle cars as we like to call them.
it wasn't till the late 90's that more hp was made by computer tuning the cars, redesigned engines and keeping emissions down to the standards in place. smaller engines today make as much if not way more power than the 60's or 70's, cui to cui that is side by side comparison of the same or close to cui.
a stock 350 in the early 70's only made like 200 hp, look at our 3800 engines we are making that and more today with 2 cly less and better mileage.
take a 74 vega 4 banger, really i mean take it, lol it was a dog, look at a honda 4 banger today, its got more power than the old gm 4 cly ever did. and runs better and longer.