REPORTING on the progress of the Cooperative Fuel Research, the author considers first the general subject of engine acceleration and then describes the test equipment and procedure of the present investigation. Discussing the degree of accuracy essential and before presenting the results obtained, he calls attention to the determination of a change in engine-torque of the order of 1 lb-ft. if a tachometer or a chronograph is used to determine acceleration. The smallest change in engine-speed that could be detected by the equipment used in this investigation was 2½ r.p.m. per sec., which is equivalent to a torque of about 2 lb-ft.The calculation of theoretical acceleration is explained. A description of the first series of engine tests, consisting of a comparison of the maximum acceleration obtained with three different carbureters used without accelerating wells, is included. A series of tests was made, using one of these carbureters, to ascertain the effect of changing jacket-water temperature alone. A somewhat similar set of tests was made in an effort to determine the effect of intake-manifold temperature, and the results are presented. The effect on performance of injecting various amounts of accelerating charge was determined also for each of the carbureter adjustments. Engine tests made recently in an attempt to determine the cause of the leaning of the mixture when the throttle is opened suddenly are analyzed, as well as the subject of flow of liquid fuel along the intake-manifold wall. Methods of determining the moment of inertia are presented in the Appendix.It is stated in the discussion following the paper that the velocity of the fuel mixture is a very important factor, and some experiments are cited that seem to corroborate the statement. Other subjects discussed include the apparent lag and subsequent recovery indicated by the charts, the variations in the duplicate runs, and the difficulty of obtaining consistent results when trying to measure engine acceleration.REPORTING on the progress of the Cooperative Fuel Research, the author considers first the general subject of engine acceleration and then describes the test equipment and procedure of the present investigation. Discussing the degree of accuracy essential and before presenting the results obtained, he calls attention to the determination of a change in engine-torque of the order of 1 lb-ft. if a tachometer or a chronograph is used to determine acceleration. The smallest change in engine-speed that could be detected by the equipment used in this investigation was 2½ r.p.m. per sec., which is equivalent to a torque of about 2 lb-ft.The calculation of theoretical acceleration is explained. A description of the first series of engine tests, consisting of a comparison of the maximum acceleration obtained with three different carbureters used without accelerating wells, is included. A series of tests was made, using one of these carbureters, to ascertain the effect of changing jacket-water temperature alone. A somewhat similar set of tests was made in an effort to determine the effect of intake-manifold temperature, and the results are presented. The effect on performance of injecting various amounts of accelerating charge was determined also for each of the carbureter adjustments. Engine tests made recently in an attempt to determine the cause of the leaning of the mixture when the throttle is opened suddenly are analyzed, as well as the subject of flow of liquid fuel along the intake-manifold wall. Methods of determining the moment of inertia are presented in the Appendix.It is stated in the discussion following the paper that the velocity of the fuel mixture is a very important factor, and some experiments are cited that seem to corroborate the statement. Other subjects discussed include the apparent lag and subsequent recovery indicated by the charts, the variations in the duplicate runs, and the difficulty of obtaining consistent results when trying to measure engine acceleration.