Intake system of engine

An intake system of an engine, the intake system comprising:

• an engine including cylinders each communicating with an associated one of intake ports which are opened and closed by intake valves;
• and
• an intake manifold attached to a side portion of the engine, the intake manifold including:
• a surge tank defining a volume chamber;
• and individual runners having (i) upstream end portions connected to the surge tank, and (ii) downstream end portions connected to the intake ports, the individual runners defining individual intake passageways each connecting an associated one of the cylinders to the volume chamber, wherein
• each of the individual intake passageways includes:
• a first route including (i) a first upstream passageway extending from the volume chamber, and (ii) a downstream passageway continuing from the first upstream passageway and connected to the one cylinder, the first route having a natural frequency, of an air column, which is synchronized with a first revolution higher than an engine revolution for maximum torque such that a dynamic supercharging effect is obtained at the first revolution;
• and
• a second route including (i) a second upstream passageway extending from the volume chamber and continuing to the downstream passageway, and (ii) the downstream passageway, the second route having a natural frequency, of an air column, which is synchronized with a second revolution higher than the engine revolution for maximum torque such that a dynamic supercharging effect is obtained at the second revolution, the second upstream passageway being different from the first upstream passageway, and the second revolution being different from the first revolution,
• the first and second routes are always open regardless of a running state of the engine,
• the first upstream passageway and the second upstream passageway communicate, respectively through a first opening and a second opening, with the volume chamber, the first and second openings being open on a side face of the surge tank farther from the engine,
• the first and second openings are arranged in a direction of a cylinder axis of the engine, and
• a difference between the first and second revolutions is set lower than or equal to 15% of a maximum engine revolution.