The instantaneous IMEP method is used to measure crankangle resolved in-cylinder friction force in a series production spark ignition engine as a function of design parameters and operating conditions. An improved telemetry system, which continues to provide data after 50+ hours of operation at speeds as high as 2000 rpm, is presented.

Primary sources of error associated with the technique will be presented. These include intra-cycle engine speed fluctuations, the effect of thermal shock on pressure transducers, the effect of connecting rod force calibration and measurement error. The instantaneous IMEP method is used to measure crankangle resolved in-cylinder engine friction as functions of engine speed and coolant (oil-film) temperature. Both crank-angle resolved and cycle-integrated results are compared.