340 Demon

.got a built 340 in a 71 Demon, it has about 13.5 to 1 compression ratio, if I run 91 octane fuel in it, it seems to run hot (210 deg.) on a 60 degree day, Ive got a 160 degree high per. thermostat in it. Electric fan w? stock radiator. Will running that low octane fuel in this motor make it run hot? Thanks