Blackwood, A., Kass, C., and Lewis, O., "Multicylinder Engine Detonation and Mixture Distribution," SAE Technical Paper 390138, 1939, doi:10.4271/390138.
PRESENT-DAY cars are not capitalizing on the continued efforts of the petroleum industry to provide better fuels, the authors believe. The wide differences found in the octane-number requirements of individual cylinders, plus the failure to obtain uniform mixture distribution from cylinder to cylinder without resorting to fuels of aviation-grade volatility have led them to reach this conclusion, they explain.The probability that significant reduction in the average antiknock requirements of cars might be effected without making any major changes in the engine is indicated by a survey of the technical literature, they point out. The extensive studies of ignition-system characteristics and gasoline-mixture distribution as affecting detonation reported in their paper bring out the following pertinent points: 1. Variations actually occurring in the spark advance from cylinder to cylinder may vary the octane-number requirement of individual cylinders by about 10 points. 2. With perfectly synchronized spark advance to all cylinders, the variation in mixture strength reaching the individual cylinders during full-throttle operation may still cause a variation of about 15 points in octane-number requirements of the individual cylinders. 3. With the particular test engine used, air-fuel mixture distribution could be improved markedly only by going to excessively high fuel volatility. 4. Care in assembling cars at the factory could bring about an average decrease in octane-number requirement of several points. This decrease, in turn, could be utilized in future designs to permit of higher compression ratio and increased efficiency.