A deceleration method was employed to measure the friction loss in a 2-Stroke spark-ignition engine for a racing boat. In order to reveal the effect of the friction loss on the acceleration operating characteristics, a transient operation test system was developed in a usual performance test setup. By adjusting the input current into the field coil of the eddy-current dynamometer, the acceleration operation behaviors were mostly simulated except for the initial rapid acceleration. Two kinds of pistons having different skirt dimensions were applied to the deceleration test to obtain the friction loss. These pistons were also applied to the acceleration operation test, and it is shown that the engine friction effect could appear in the acceleration operation characteristics according to that predicted from the friction measurement results on the whole.
