An improved muffler including a body 2 with an exhaust inlet 3 in the form of a porous pipe enclosed in s second porous pipe 31 for diffusing exhaust gases into the interior of body 2. A pair of pipes 5 introduce ambient air into the discharge region of the muffler. A constricted discharge opening 41 of the body 2 encircles the pipes 5 and confine helical vanes 51 which impart a helical path to the exhaust gases just before mixing with ambient air from the pipes 5. A venturi section 6 with a bell shaped outlet 62 completes the tailpipe section 4. An auxiliary air inlet 43 to the venturi 6 adds additional ambient air to the final outlet via ports 63. In an additional embodiment (FIG. 8), the venturi section 113 is within the muffler body 100. A constricted tube 121 provides a direct path for a portion of the exhaust gases while the major quantity of exhaust gases traverse the helical paths defined by the vanes 123.