Abstract: An adaptive valve assembly includes a pipe defining a passageway for conducting engine exhaust gases, a pivot shaft supported by the pipe, and a valve body coupled to the pivot shaft. The valve body is moveable between an open position where exhaust gas flow through the passageway is increased and a closed position where exhaust gas flow through the passageway is reduced. A spring biases the valve body toward the closed position. The spring includes a plurality of coils that have torsional displacement relative to each other as the valve body moves between the open and closed positions. A torsional damper feature is associated with at least one coil of the plurality of coils to provide torsional spring damping.