Wave effects in exhaust systems can strongly influence the performance of an engine. Predictions of pressure-time variations at the exhaust valve by graphical methods, based on experience and the assumption that exhaust pulses will act as sound waves, have been of no design value with multicylinder engines. Now a numerical method, developed from the graphical has been programmed for a computer making possible rapid calculation on nonsteady flow properties of an exhaust system. When augmented by experimental testing of three disparate exhaust systems, such calculation proved useful in the design of exhaust systems for multicylinder automobile engines. This Paper describes the engine investigations of the three systems involved and the derived design conclusions.