[wizardwizard]

i think this refers to the air pressure in the intake tube while at 1500 rpm @ 25 mph and how this pressure would change immediatly when you hit the gas pedal it starts taking in more air wich means less air would be in the intake area and more air in exaust.
when you press the gas, the pressure changes, the gas is held up by water pressure from the tank as long as you have gas, the air pressure is not as stable as this water pressure so you could have a situation where you cant go any faster cuz you cant get enough air into the intake like if you had a front air dam.
the pressure of the air intake fluctuates in an unstable way as your engine uses more and less of it compared to the flow of the gas which is constant because water (liquid) cannot be compressed or decompressed physically (maybe with chemical reaction)
by using a ram air or cold air, you ensure that the intake air pressure stays up when it is being sucked at varying amounts and changing in a way that is unstable compared to the gas intake pressure which is constant.
it makes it easier for the engine and computer to keep the right fuel air timing ratio if it can control the amount of air and gas it is using with instruments that work 100% of the time.