In this paper the 1-D modeling of flow through the assembly of valve and port in internal combustion engines is discussed. Three dimensional effects and flow losses close to the valve are accounted for through the experimental effective area, determined at a steady flow bench. The steady flow bench is standard equipment, widely used for engine design and development. The classic method is adequate to the purpose as long as the objective of measuring the effective area is a comparative process for the experimental improvement of the flow through the valves. On the contrary, if the effective area is used for engine cycle simulation, the experimental results must be considered with care.It is demonstrated in this study that, for the outflow from a cylinder to a valve, standard experimental practice can sometimes produce a significant error on the flow rate predicted by simulation. The paper proposes a correction on the valve effective area, based on the geometry of the system and one handbook value.An experimental campaign has been carried out at a traditional flow bench on the head of a high performance four stroke engine in order to validate the proposed theory and to gain a better insight on the flow patterns. For this particular engine, the influence of the throttle plate on the flow through the intake valve is assessed. Concerning the exhaust system, the steady test setup is discussed, with the help of experiments.A simple theory has been built up in order to derive, from standard experiments, values of corrected effective areas to be introduced in the model of the intake system. Experiments have been integrated by data provided by steady 3-D CFD simulation, and/or by handbook.Finally, the model, adjusted according to the above theory, has been applied to the 1-D cycle simulation of the engine. The corrections produce some variations on volumetric efficiency and pumping mean effective pressure, at both partial and full load. Large differences have been found in pressure and mass flow rate traces, particularly at partial load.