The Comprex was developed by BBC to the series production stage in cooperation with various automobile manufacturers.(Ref. 1-6)In order to subject the consequent design of the pressure wave machine components to realistic operating conditions twenty-seven vehicles of identical type (Fig.1) were put into on-road operation by BBC. The vehicles have been in use since the middle of 1983. All vehicles are powered by a 1.6 ltr. swirl chamber engine which was designed to be turbocharged.