On actual gasoline turbocharged engines it is common to use a compressor by-pass valve in order to solve the compressor surge problem when the throttle pedal position is released and closes rapidly. The paper deals with a methodology based on experiments to measure the discharge coefficient of an integrated compressor by-pass valve, to understand the possible difference between the steady flow test bench and turbocharger test bench discharge coefficient measurements. To determine if there is some compressor outlet flow field influence due to compressor blades rotation that could modify the discharge coefficient measurement, compared to the steady flow test bench measurements, a fully instrumented turbocharger was used to measure the difference between steady flow test bench and turbocharger test bench discharge coefficients results. Effects of different boundary conditions on turbocharger test bench tests and how they affect the discharge coefficient measurement are also presented.Furthermore, the measured compressor by-pass valve discharge coefficient on the steady flow test bench is used as input for an 1D model in order to verify or modify the compressor by-pass valve geometry design. The model is used to modify the compressor by-pass diameter and analyze the influence in the compressor behavior during a typical throttle pedal release situation.The results should lead to design improvements and better understanding of these integrated compressor by-pass valves in order to avoid compressor surge in gasoline turbocharged engines during a throttle pedal release situation.