An existing 4 stroke-cycle gasoline engine has been partially modified without dynamically changing its mechanism for the purpose to utilize compressed air as an alternative energy source. The principle is to mechanically control the compressed air flow through the intake and exhaust valves every revolution of the crankshaft by modifying the camshaft cam's lobes, which changes the engine operation from 4 strokes to 2 strokes cycle mode. In the previous investigation the principle was verified with a current 50 cc motorcycle modified engine and the pressure behavior inside the cylinder of the compressed air engine was evaluated. It turned out that the back pressure, which is defined as the positive pressure left in the expansion chamber while the piston is moving back from the bottom dead center to the top dead center, has high influence on the performance of the compressed air reciprocating engine. In this investigation the same pressure and performance measurement were conducted for the modified engine assembled the cylinder with side holes drilled to confirm an effect on the back pressure relief, thus verifying one of the effective solutions to improve the performance of the compressed air reciprocating engine.