This calculator isolates the Otto Cycle "Power Stroke" and computes some values from TDC to BDC at 10 crankshaft degree increments.
Piston Pressure is the NET pressure on the piston top. It starts at an arbitrary absolute 100PSI times compression ratio (C.R.) less atmospheric pressure (14.7psi). Rod Angle is the angle in degrees between the bore centerline and the line between the small & big rod ends. Side Thrust is the sidewards force on the piston due to Rod Angle. Rod Force is the downwards force on the connecting rod due to NET Piston Pressure over the area of the piston top through the Rod Angle. It is coincident with the connecting rod centerline acting on the crank pin journal centerline. Effect Lever is the effective lever arm in inches. Its maxiumum value is half of stroke which occurs at the optimum crank angle. Effect Torque is the Rod Force times the Effect Lever. AUC TQ is the average Area Under Curve of Effect Torque from TDC to BDC.
Note that after EVO (advertised), the Piston Pressure starts to degrade more than just due to piston drop (increasing cylinder volume) because exhaust gas is starting to leak out the exhaust valve. After EVO (@0.050), the Piston Pressure is effectively zero because the exhaust gas is exiting out the exhaust valve and no longer pushing the piston down.
Also note that to compare engine-to-engine the C.R. must must be the same (not the default from the pull down) since it is fixed at an arbitrary 1000 times C.R.
Also note that in the complete Otto Cycle the Piston Pressure will also be dependent on the inlet tract (carb CFM, intake manifold and intake port flow) and intake valve cam profile. See "Otto Cycle Calculator" for that computation.