Search Results

The recent introduction of lower compression ratio engines and the concurrent marketing of unleaded and low-lead content gasolines of generally lower octane number made it appropriate to investigate the interrelationships of engine performance and gasoline octane quality using the “new” engines and fuels. Programs were carried out to compare fuel economy and acceleration performance of eight matched pairs of 1970 and 1971 automobiles. In addition, octane requirements were obtained on 43 1971 cars with 3,000-12,000 deposit miles. A total of 146 unleaded, low-lead, and leaded regular gasolines obtained at service stations throughout the country were analyzed, and the road octane performance of these gasolines was determined using 1970 and 1971 cars designed for regular gasoline.

The influence of driving procedures and extraneous car noise on perception of engine knock has been studied with late model cars. Year to year changes in reports of knock by both customers and raters and changes in octane requirements were also reviewed. Customers generally accelerated cars less vigorously and tended to perceive knock less often than raters. However, in cars that had maximum octane requirements at part-throttle, customers perceived knock about as frequently as raters. Octane requirements, as determined by raters, were reduced by about 2 Research Octane numbers when the car radio was turned on and the windows closed. Both customers and raters reported more knock with 1975-1977 model cars than with earlier models. Since 1975, octane requirements of certain car models tended to be adjusted to the octane quality of available gasoline.

Annually, the Coordinating Research Council (CRC) sponsors a nationwide survey of octane number requirements for current model passenger cars. In this review, based on surveys from 1965 through 1974, trends in octane number requirements reflect changes in engine design and exhaust systems to meet the legislated limits on emissions. The average requirement dropped approximately 5.5 Research octane numbers over the ten-year period with the most dramatic drop of approximately 3.0 octane numbers in 1971 when car manufacturers recommended use of 91 octane gasoline. The trends toward lower average requirements since 1971 have been determined with both leaded and unleaded fuels. Incidence of surface ignition knock and rumble was about one per cent in 1965 and tended to disappear after 1971. The average spread of octane number requirements between 10 and 90 per cent of cars satisfied increased about 2.5 numbers over the period.