I don't recall most of the octane numbers from back then but here is some info on the old Sunoco Leaded Fuels:
* leaded fuel had higher octane numbers compared to todays unleaded, regular was 89 octane.

190 - subregular
200 - regular 89 octane
210 -
220 - mid grade
230 -
240 - premium (ethyl)
250 - premium +
260 - super premium 102 octane

I remember running 260 back then in my stock compression 327 and thinking it was making the motor run better (faster) but I doubt that was the case. Of course back then it was around 35 cents a gallon and the uneducated thinking was the higher the octane the better. The car also ran just fine on 200 without knocking.

While higher octane may produce more BTU's, that is only true if you achieve complete combustion. Since high octane burns slower, using too high an octane will result in the exhaust valve opening prior to the complete combustion of the fuel, resulting in a loss of useful BTU's. This is all dependant on the specific engines cam, valve and ignition timing.

One example, I have an 07 model cage with a 10.5:1 compression ratio that runs fine on regular or premium fuel, but that is accomplished with computer controlled variable ignition timing. Or Harleys arn't there yet, thank God.

 

My 1970 426 Hemi Cuda loved the Sunoco 260...