We have tried to convert a petrol engine into a compressed air engine back in our graduation project. At that time we only measured the RPM of engine using tachometer and pressure of compressed air using pressure gauge. Now, we need to know the power of wngine at those readings. As the setup is long gone and we cannot duplicate the trials again, can you please suggest me how to determine the torque by mathematical calculations? I am thinking of using following series of formula: Torque (of engine) = Force (on piston) x Radius (of crank travel) Force (on piston) = Pressure (of air) / Area (of piston head) Please tell me that can this calculation be justified?