The loss of momentum of the gas-core inside inlet manifolds of four-stroke engines is characterized by loss coefficients. Usually these coefficients are obtained by experimental investigations of the flow through cylinder heads under steady-state conditions. The dynamic behavior of the gas motion under real conditions due to acceleration and vibration of the gas-core as well as the influence of the gas motion due to the exhaust can not be described by these coefficients.Therefore a basic investigation of the unsteady flow under real engine conditions has been performed. The aim was to develop a simple method to characterize the inlet flow behavior under real conditions and to define a dynamic loss coefficient.The mass flow rate was determined by time resolved pressure data inside the suction pipe and a simple numerical calculation method considering unsteady flow conditions. The verification of calculated flow velocities was performed by using Particle-Image-Velocimetry.A theoretical charge of the cylinder, calculated with pressure data in the combustion chamber, was not suitable to determine a loss coefficient due to motional behavior of the gas core. The mass flow obtained dynamically under real operating conditions gives further information about the efficiency of charge and the unsteady gas dynamics. The numerical integration of the mass flow leads to the volumetric efficiency of the cylinder.The experimental setup could be fitted easily to any engine to investigate and to optimize the inlet manifold.