Air intake system for multi-cylinder engine

An air intake passage structure for an engine comprising:

• at least three or more of a plurality of cylinders that are arranged in an array;
• a plurality of intake ports that respectively communicate with the plurality of cylinders;
• and
• an air intake passage that is connected to each of the plurality of intake ports, wherein
• for each of the plurality of cylinders, the plurality of intake ports include a swirl control valve (SCV) port that is configured to reduce a flow rate of flowing gas via a swirl control valve,
• the air intake passage has:
• a plurality of independent passages that are respectively connected to the plurality of intake ports;
• a surge tank, to which upstream end portions of the plurality of independent passages arranged in an array according to an alignment order of the corresponding cylinders are connected;
• and
• a plurality of upstream passages, a downstream end portion of each of which is connected to the surge tank, and each of which introduces the gas into the surge tank, and
• the plurality of upstream passages are arranged with a space being interposed therebetween in a cylinder array direction, and, when the surge tank is viewed in a cylinder axis direction, the plurality of upstream passages are connected to the surge tank on extension lines, each of which extends from the upstream end portion of one of the independent passages connected to one of the SCV ports to an opposite side of the plurality of cylinders.