I am trying to understand some effects of pressure differences and air density particularly as it relates to the good ole american made V-8. One of my questions: What is the "speed" of air when a pressure differential is equalized? Assume I have a cube that is exactly one cubic foot in size. If the cube is in the room with me, after I close the lid I assume the pressure in the cube is the same as the pressure was in the room (~29.92inHg). If I remove 1 cubic foot of air from the cube (Can I?), what is the pressure in the cube? If I open the lid for 1 millisecond, is the cube instantaneously filled with air? Does it matter how large the opening is that I use to let air into the cube? What if the lid is only opened for 1 nansecond? Is the vacuum completely gone? In an engine, there are many restictions to getting air into the cylinder: Air filter, tubing with bends, throttlebody, Intake manifold, cylinder heads, valves, etc. Is the speed of the air related to the pressure differential between the cylinder and the intake manifold? Does piston speed have any impact on the speed of the air? Is the cylinder ever not completely full of air? In other words, does the density simply vary based upon the amount of time available to fill the cylinder (RPM), restrictions, density of incoming air, etc? I apologize for all the questions and my ignorance. I am just trying to better understand how my engine actually works. Thanks.