PURPOSE: To positively form a laminated tumble flow without reducing the flow speed of intake air by forming, in an intake port for forming a part of an intake passage a width widened part, in which the upper half is expanded larger than the lower half, and a connection part, in which the lateral width and cross-sectional area are specified on its upstream side.
CONSTITUTION: An intake passage is formed so as to make the air flow flowing into a fuel combustion 30 a tumble flow. An intake port forming a part of an intake passage is branched off into two intake port parts 46A, 46B at a branch part 46C. In this case, the intake port is formed of a widened part 11, in which the upperhalves 46A-1, 46B-1 are widened larger than the lower halves 46A-2, 46B-2, and the center of the intake port is eccentrically shifted to the upper half, and of a connection part 12 connected to the upstream side. The lateral width and cross-sectional area of the connection part 12 are set to the same as the lateral width and cross-sectional area of the widened part 11, and the lower half of the connection part 12 is eccentrically shifted to the side of the upper half to be connected to the width widened part 11. Thus, lamination of respective tumble flows can be strengthened, and torque-up and low fuel consumption can be also attempted.
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