This paper describes a comparison between calculated and measured pressure traces and air mass flows through a family of inlet manifold geometries. It is shown that a non-linear wave action calculation technique, based on the method of characteristics, can accurately predict the detailed variation of pressure in the manifold over a broad range of engine speed: it can also accurately predict the mass flow.It is shown that it is necessary to include end effects for the various pipes in order to obtain realistic predictions. The mass flow can be predicted to better than 2% over the majority of the engine operating speed, although the accuracy decreases slightly at the tuning speeds. This reduction in accuracy is probably due to the increased losses resulting from the higher velocities and flow reversals occurring at the tuned speeds. It is also shown that tuning of the system occurs when the natural frequency of the manifold causes an increase in cylinder pressure when the inlet valve closes.