A schlieren-streak optical system for measuring instantaneous exhaust gas velocities was developed and tested using a CFR single cylinder spark-ignition engine. Local density gradients which move along with the local fluid velocity in the exhaust gas flow, were used as velocity tracers in the schlieren system, and their motion parallel to the exhaust pipe axis was recorded by a streak camera. The performance of the schlieren-streak system was checked with a calibrated hot-wire anemometer by comparing the instantaneous exhaust gas velocity data obtained by both methods in a motored engine. The agreement between the two methods was within ± 10%.The schlieren-streak velocity data were also compared with the results of a computer simulation based on one-dimensional unsteady gas flow. The computed instantaneous cylinder and exhaust pressures were within ± 8% of the measured values. The agreement between measured and computed instantaneous exhaust gas velocities was within ± 10%.