Abstract: A noise attenuating device is disclosed combined with the air induction system of a multicylinder internal combustion piston engine, which includes an expansion chamber connected into the air induction system with an inlet and outlet. A first and a second tuning tube is concentric with the inlet and outlet, respectively, and are axially movable relative each other to assume either an underlapped or an overlapped configuration. The tubes are relatively driven axially to be shifted between the overlapped configuration at low engine speeds (under 2500 rpm) and an underlapped configuration at higher engine speeds to more effectively attenuate the characteristic harmonic orders of induction noise at these respective engine speed ranges.

Abstract: A method and device are disclosed for tuning an air induction system of an internal combustion engine in which an expansion chamber is combined with a Helmholtz resonator tuned to resonate at the engine speed whereat the expansion chamber would otherwise cause an engine torque decline, the combined effects tuning the system over the entire operational range of speeds of the engine.