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Three-dimensional computations are performed to investigate the scavenging characteristics of poppet-valved two-stroke engines. The new subroutines are developed to handle various valve shrouds. Visualization of scavenging flow on a modified two-stroke transparent cylinder engine is used for validation and compared well in flow pattern. The flows in engines with different configurations are simulated at a speed of 5000 r/min. The stroke bore/ratio and valve arrangements were considered to investigate their effects on the scavenging flows. Additionally, valve timing and boost pressure have also been studied. The results show that stroke/bore ratio of 0.4 to 0.6, shroud angle of 69° to 108°, turn angle of shroud of 18° to 28°, average tumble ratio of 1.2-1.6 were found to be the optimum range for effective scavenging.