OK, lets see if I can clairify my opinion:
What I am saying is that in a NA engine, where no movement of the piston is present, and the intake valve is open, we have a ballance of pressure on both sides(14.7 psi at sea level). when the piston moves downward, it creates a "negative pressure" or vacuum in laymans terms. This difference in pressure causes the outside air to be drawn in. So in MY opinion, it is the creation of "negative pressure" that causes the air to move, not just the static pressure of atmospheric pressure that moves itself. This leads me to the hypothosis that it is the VACUUM that is the action, and the air movement is the reaction.
As far as our experiment, we were using an absolute pressure gauge, and slow motion video of the needle. of course we never reached lower that 7 psi of "negative pressure", as those who know much about science, it is near impossible to actually attain 0 psi in most scientific experiments that are done in a classroom lab. the lowest we ever did using a pump was 4 psi before the cylinder cracked.(we were using a glass cylinder with a small amount of mercury in the bottom to see if we could detect any "movement")
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Originally Posted by CrazyBill5280
If it was just the piston suction alone then I would think a naturally aspirated engine would make the same power regardless of altitude. Yet an engine makes 18% less power here in Denver than at sea level.
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The reason you have less power in a NA engine as nothing to do DIRECTLY with the atmospheric pressure, but the DENSITY of the air that is draw into the engine. Yes A.P. is lower in denver, but the REASON it is lower is that the air in Denver is less dense. DENSITY of the air is what makes the difference in engine power, that is why in racing, colder weather is prefered, because colder air is more dense, and this gives the engines more power.