An experimental investigation developed on a small turbocharger compressor for automotive application is presented. The study focuses on the effects of internal heat transfer on compressor efficiency, evaluated for different values of inlet pressure, mass flow rate and compressor rotational speed. Infrared thermography has been used to evaluate the heat transfer rate from the turbine to the compressor and to correct the measured compressor diabatic efficiency. The approach has been validated by performing additional measurements under quasi-adiabatic conditions, avoiding map distortion due to heat transfer. Simple relationships for the prediction of internal heat transfer, validated against the measured values, have been proposed. The practical significance of the results, with reference to turbocharger compressor performance, is outlined. (C) 2017 Elsevier Ltd. All rights reserved.