To give a little background I have machine tool training but not much other than what I have taught myself in general physics. Its a VERY interesting subject for me and I have thought about going back to college just to take a course or two relating to it. I come up with various ideas I would like to test out but cant always get my head around good ways to plan a build calculation wise. One of my current projects is a CO2 or Air powered engine. I am familiar with measuring and caution involved with high pressure but could use some help in sizing calculations for components. I would like to try to make a small engine that uses pressurized air (or CO2) as the working fluid but am having some issues getting started with designs. I have been reading a good bit on the bore and stroke's effect on performance but many of the calculations I could find deal with IC engines. How do I calculate for a certain pressure input how bores and strokes will react power and RPM wise? I know the shorter stroke will tend to have a faster RPM but lower torque but how do you come up with an optimal number to start testing at? For example lets say I have 1500 PSI (gauge or absolute whatever is easier to calculate) as an input and want the engine to comfortably put out 60 HP @ 2200 rpms in one cylinder with (60 x 5252)/2200= ~143 ft/lbs torque. Another big issue is the flow rate in order to fill that combination of bore and stroke in the right amount of time. So 2200/60=~36.6667 rps and 1s divided by 36.6667 is ~.0273. If I did that right one revolution happens about every .0273 seconds. This means that I have half that time (now 13.65ms) to get the pressure in the cylinder for the power stroke. I need to know how to figure the bore and stroke combination in order to finish this calculation though. All of this is just an example to get some formulas started but was the best place I knew to start. Thanks for any help.