Some New Aspects of Deposit Effects on Engine Octane Requirement Increase and Fuel Economy

Historically, the increase in octane requirement (OR) of a car engine with mileage was thought to be caused almost entirely by combustion chamber deposits. Tests with recent model V-8 engines, using a special technique for octane rating the individual cylinders of the engines, showed that certain intake-port-area deposits can have as great an effect on OR as combustion chamber deposits. Fuel consumption tests with these same engines showed that combustion chamber, intake valve, and particularly intake port deposits have a beneficial effect on fuel economy; that is, physically removing these deposits from the engines increased fuel consumption by up to 9%. The probable causes and implications of these findings are discussed.