<p>The length of a partition wall of a suction port is determined such that the ratio between the length of the partition wall and the center-to-center distance between adjacent suction valves is not less than 0.45 and not more than 0.72. An injector is installed on the upper side of a throttle body. The angle f of installation of the injector is set to not less than 42 degrees and not more than 55 degrees. The injection start timing of the injector is set to within the period in which the suction valve is closed.</p>
