Abstract: A multiple-cylinder engine has first and second groups of cylinders, the firing order being set so that the cylinders in each group do not fire one after another. An intake system for the engine has first and second groups of discrete intake passages which communicate with the respective cylinders in the first and second groups at their downstream ends and with first and second branch intake passage at their upstream ends. A circular passage communicates with the discrete intake passages at their intermediate portions so that all the discrete intake passages communicate with each other through the circular passage, and an on-off valve opens the circular passage when the engine speed is higher than a predetermined value and closes the same when the engine speed is not higher than the predetermined value.

Abstract: An intake system for a multiple-cylinder engine has a plurality of discrete intake passages which are substantially equal to each other in length and are connected to the respective cylinders at their downstream ends. The upstream ends of the discrete intake passages are merged into an integrated chamber, and an upstream side intake passage communicates the integrated chamber with the atmosphere. The integrated chamber has an upstream side end face and a downstream side end face, and the cross-sectional area of the integrated chamber increases from the upstream side end face to the downstream side end face, the upstream side intake passage having opening into the integrated portion in the upstream side end face, and the discrete intake passages respectively having openings into the integrated chamber in the downstream side end face. The area of the upstream side and downstream side end faces of the integrated chamber S.sub.0 S.sub.

Abstract: An air intake device of an engine has intake pipes connected to each of the engine cylinders divided into first and second groups to prevent the continuance of the intake strokes of adjacent cylinders. A first connecting cavity connected to the first group of cylinders and a second connecting cavity connected to the second group of cylinders are arranged in parallel with each other, for effecting supercharging by utilizing the dynamic effect of intake air into each cylinder. A first communicating passage is connected at one end to a longitudinal end of the first connecting cavity and at the other end to a longitudinal end of the second connecting cavity. A second communicating passage arranged on the same side as the first communicating passage is connected at one end to a side of the first connecting cavity and at the other end to a side of the second collecting cavity. The effective passage length of the first communicating passage is shorter than that of the second communicating passage.