PURPOSE: A valve mounting structure of a variable intake system is provided to improve the output of an engine according to the length change of an intake passage over the whole operation area of the engine by reducing a dead volume generated in closing the valve in a middle-low speed area of the engine. CONSTITUTION: A variable intake system of an intake manifold(30) comprises an auxiliary tank(34) and a connection pipe(35) installed at the lower part of a runner(31) connecting between a surge tank(32) and an intake port to shorten a passage for the intake air when the engine is in a high speed area and a valve(40) disposed in the middle of the connection pipe to control the passage for the intake air. A preserved length is 1.2¯1.4 times as long as an inlet length of the valve when the valve is opened. The closing angle of the valve is set obliquely to a runner central line(O) within 8¯10 degrees.
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