I am interested in the higher octane resistance to burn vs. longer burning idea. Thank you for the links and writing, Dan. This is new thinking for me, but it makes sense. For one thing, we might expect that if the fuel is more highly refined, then the variation (spread or distribution) of gasoline molecules/sizes will be smaller, and thus the ability to preignite will be lower. Lower octane rating fuel might have a wider range of molecule types, so some of the smaller (or differently shaped) molecules will preignite more easily and start all the other ones burning, causing knock.