Vehicle Octane Number Requirement versus Altitude - Another Look

Historically, vehicle octane requirements decrease with increasing altitude due to the effect of changing barometric pressure on in­duction and ignition management system func­tion. Recent advances in engine technology designed to reduce emissions and improve fuel economy of vehicles at high altitudes could result in minimal octane requirement change with changing altitude. In order to confirm the effect of these technology changes, Petro-Canada determined the octane requirements of twenty 1987-88 model cars and light trucks at high and low altitude locations. Seventeen of these were equipped with altitude compensation sensors. Contrary to previously published data, we found that the octane requirements of the 17 compensated vehicles were reduced, on average, by 0.5 (R+M)/2 per 1000 ft, increase in altitude. Although we expect that octane demand in high altitude areas will rise as the penetration of these vehicles progresses, the magnitude of the increase is not as great as previously estimated.