Exhaust device for internal combustion engines

An exhaust device for an internal combustion engine with an external envelope comprising in the direction of flow of the exhaust gases, a first section defined by a progressively increasing cross-section, a cylindrical section following said first section the diameter of which is equal to the greater diameter of said first section, and said cylindrical section being further defined with its interior provided with a streamlined member with an ogival or conical surface which is substantially coaxial with said cylindrical section and the vertex of which is upstream, exhaust gases flowing without any perturbation of the fluid stream inside said first section and, after, through a progressively decreasing cross-section, between the streamlined member and the cylindrical section of the envelope.