INTERNAL COMBUSTION ENGINE SILENCER

A muffler for internal combustion engines, in order to achieve a high attenuating effect without reducing the attenuating effect in the high revolution range of the engine, comprising one or more expanding chambers 11 through 13 formed in a muffler 1, an inlet pipe 5 which opens into a expanding chamber 11 and introduces exhaust gas into the muffler 1, and an outlet pipe 6 which opens into other expanding chamber 13 and introduces exhaust gas out of the muffler 1. In the muffler, the exhaust gas discharged through an aperture 5a of this inlet pipe 5 is inverted once or more times in the muffler 1 and is introduced into an aperture 6a of the outlet pipe 6. In a contraflow area L2 in which the flowing direction C of exhaust gas flowing in the expanding chambers 11 through 13 and the flowing direction E of exhaust gas flowing in the outlet pipe 6 are not the same, interference holes 7 composing of a plurality of small holes communicating with the expanding chambers 11 through 13 are bored in the outlet pipe 6. The aperture area of the small holes 7 is kept at not less than 1% but not more than 5% of the surface area of the outlet pipe in the contraflow area L2.