This study investigated a modified intake and exhaust system for piston-type compressed air engines. A conventional 100-cm(3) four-stroke internal combustion engine was modified to a two-stroke compressed air engine and its output power and fluid properties at various intake pressures and rotational speeds were examined. The torque output, airflow rate, and cylinder pressure were recorded; these values reflected the fluid characteristics of the compressed air engine during operation. The conventional engine design uses a cam mechanism for controlling the intake and exhaust valves, wherein the valves open and close gradually. To overcome this drawback, a rotary intake and exhaust system was designed in which the valves open and close quickly. This new system is operable at air pressures as high as 13 bar, and the operating cylinder pressure rises faster than it does in systems featuring the conventional cam mechanism. Air engines installed with the new rotary intake and exhaust system yield an output power of 2.15 kW and a torque of 15.97 Nm at 13 bar. (C) 2015 Elsevier Ltd. All rights reserved.