Not exactly true, the rating is a resistance to detonation, not burn speed. A higher octane may actually burn faster. Gas is a mix of hydrocarbon compounds, some evaporate early and some late. To give you an example, Track Tek 114 has an initial boiling point of 110˚ and a 100% evaporated point of 300˚. Track Tek 118, a higher octane, also starts at 110˚ but ends earlier at 250˚. There are also differences in specific gravity of fuels, which usually require a change in tuneup. When we ran it years ago, it liked to be a little richer than race fuel, if you are too rich with race gas it might explain it.