[mrtexas]

Gasoline in the 30s was very low octane, lead added a significant amount 8-10 numbers. Gasoline was mostly distilled from crude straight run gasoline and naphtha with octane in the 70s. That is why Model A and early v8 motors were such low compression ratios. Thermal cracking existed and Houdry fixed bed crackers made some gasoline out of heavier stuff. Most of the modern refinery processes to raise octane were developed in the 40s/50s like alkylation, residual coking, hydrocracking, platinum reforming, and catalytic cracking. Alkylation developed around 1940 made very high octane as it produces iso-octane(100 octane) and lead added made fighter plane aviation fuel. Today gasoline produced is up to 50% of crude oil distilled for high conversion refineries.