Dcr

"Dy-na -mic".
The output of the calculators assumes atmospheric pressure, and assume the geometry of the lobe and the affects of racker ratio and angles on motion, and assume there are no dead spaces above the piston ring, and assume a low piston speed. They do not take into account the physics of a running engine. So you are computing pressure at 60rpm. Here is a link to a page that has a great graph. Sorry I can't attach a picture from this PC:

http://performancetrends.com/Definitions/Cylinder-Pressure.htm

Go to the page and look at the graph posted there. This is a pressure graph for a cylinder during all four strokes. Note the curve up when the piston is moving from BDC up towards TDC on the compression stroke. The shape of that particular curve, before the ignition event, is crutial. Too fast a rise and you can get detonation or ping from other deficiencies. Too slow and the engine will react sluggish because the cylinder filling is not what it could be. Now as you quicken the time for these cycles (raise the rpm) you can see where that particular curve could be really affected by inertia of the exhaust blowdown event and the intake charge within the intake tract and by the larger area exposed to atmospheric pressure due to open throttle blades (more "push"). The changes in the curve due to rpm are what one should worry about. Not the actual dynamic ratio. Cranking pressure at cranking rpm means next to nothing IMO in regard to output but it can indicate problems and is fun to talk about.

PS. Disclaimer - I own Engine Analizer Pro.