SUCTION SYSTEM OF ENGINE

PURPOSE:To make it possible to generate strong swirl in a suction system where a suction passage is branched downstream of an openable valve and each of such branched suction passages is connected to each of suction ports, by specifying an opening position of an auxiliary suction passage connected to one of the suction ports. CONSTITUTION:First and second suction ports 4 and 5 having substantially same diameter are opened to each of cylinders 1 of an engine in such a manner as to be arranged substantially symmetrically with respect to a center line (1) in a lateral direction of a cylinder block. A suction passage 7 communicated with the suction ports 4 and 5 is branched into two by a partition wall 9 in such a manner as to be projected along the center line (1) before the ports 4 and 5 to form branched suction passages 10 and 11 connected to the suction ports 4 and 5. An openable valve 12 is provided upstream of the branched portion of the suction passage 7, and an upstream opening 13a of an auxiliary suction passage 13 is formed upstream of the valve 12 in such a manner as to be offset to the suction port 5 side with respect to a center line (1') of the suction passage 7, while a downstream opening 13b is formed at a position near the suction port 4 in the branched suction passage 10.