Dyno testing a stock(?) 1972 440

Higher compression always increases vacuum and smooths the idle with a bigger cam. It also increases your gas mileage at the same time as power (it is mathematically related to the "fuel conversion efficiency" of the engine). Heat from combustion also is higher meaning you have to beef up the cooling system and run a cooler thermostat. Most importantly for the car companies in the '70s higher compression puts out more NOx emissions especially if the combustion chamber isn't very "fast-burning."