SUCTION SYSTEM FOR ENGINE

PURPOSE:To obtain an average output improving effect in the whole operating region and set a flat torque type engine by generating an inertia supercharging effect and a resonant supercharging effect in rotation regions which are apart from each other to some extent. CONSTITUTION:The inertia synchronized number of rotation of an air column vibration system on the lower course sides of surge tanks 3, 4, which is determined by the length l1 and area A1 of the air intake passages 2a-2f which are connected to cylinders 1A-1F and divided into two cylinder groups whose suction strokes do not substantially overlap, is determined as N1, and the resonance synchronized number of rotation of an air column vibration system on the upper course sides of the surge tanks 3, 4, which is determined by the volumes of the surge tanks 3, 4 and air intake passages 2a-2f and the length l2 and area A2 of air intake passages 5, 6 up to a confluence part 7, is determined as N2. In this case, the N1 is set at 4,000-6,000r.p.m. as well as in a condition that N1-N2>=N1X0.15. Also, each area A2 is set to a smaller value than the sum of each area A1, i.e., A1X3.