To expand on this.
P = pressure (boost)
V = volume (flow)

and on the other side of the equation

n = quantity of air molecules (moles)
R = ideal gas constant
T = Temperature of air

So if temperature goes up, and pressure and volume are the same, then you have two options:

1. change the laws of physics and re-write the ideal gas constant
-or-
2. REDUCE the actual amount of air getting into the motor.

The inverse is the root of your question. If you lower the temperature of the air, then you can have the same boost and same CFM but have more actual air molecules going into the motor.

 

Humor me here for a minute. Now i get that colder air should be more dense. In this case. I wonder if the 1 psi that has been compressed from the turbo, then put through the IC, would have just as much o2, as the more dense(colder air), since we have not introduced any extra molecules of o2 into the system. The only way, i can see, to gain o2, would be to start with a colder ambient temp, which is where the air would start out with more o2.

...and i'm just going to throw this out there: ...but if you place a restriction inline don't you in fact increase the psi? I think of it this way. Hot air (expanded molecules) go into the endtanks, where the air is defused, then to the IC, where cooled. As it's cooled, it slows, because it takes up less volume, causing the psi drop because it's less dense, here it could exit at an increased rate becuase of a smaller outlet, which would cause the psi to rise again, and to your credit, increase the velocity.

Sometimes I think with my feet in my nose, so please share you thoughts, because mine stink sometimes.

 

On the first paragraph, you need to think of the system as a whole. The boost pressure created by the turbo is regulated by the wastegate.... which gets its 'signal' from the intake manifold. So the turbo will spin hard enough to maintain the pressure at the intake manifold at a certain value, say 20psi. The pressure is the only value that matters to the wastegate; not temperature at the intake manifold. Therefore, 20 psi @ 120F will contain a greater mass of air than 20 psi @ 200F. This is the whole point of an intercooler of course. Also, 20psi at the turbo does not equal 20psi at the manifold; I think someone measured a 6psi pressure drop from the turbo to the manifold on a stock evo at max flow conditions; you have to quantify the flow conditions because pressure drop is directly related to flow velocity.

You're slightly confused in your second paragraph. If you place an in-line restriction in the line of a compressor outlet (so turbo outlet in this case), you will get an increase in pressure between the compressor outlet and the restriction for a given compressor speed. But you will also lower the mass flow rate of air. Also, you'll have a pressure drop across the restriction.

So, to relate to what you're thinking about, the IC is a flow restriciton. Lets say at a flow rate of 400 lbs/min of air (should really use velocity, but anyways), you get a pressure drop of 3psi going through the intercooler; this is due to flow resistance due to friction, entrance/exit effects (going into and out of the IC), etc. But, you're asking for 20psi at the intake manifold. So now, the turbo has to make 23psi of pressure at the turbo outlet so that you get 20psi at the intake manifold.

So basically, reducing flow restrictions between the turbo in intake mani is a good thing. So that's why LICP are so popular. Basically, by reducing the pressure loss, the turbo doesn't have to work as hard(also reducing how much it heats up the air) to give the same boost and flow rate which all equals more power.

Another reason why cold air entering the turbo is doublely (is that a word?) important. If you look up the equation for compressor power, it's basically:

power = (temp in)*(mass flow rate)*(pressure ratio^(k-1/k)) *Cp.

The 'power' is what you get from the turbine wheel to spin the compressor wheel. For equal power, if you lower the temp of the air entering the turbo, you can get either: more mass flow rate for a given pressure ratio (boost pressure), or more boost pressure for the same mass flow rate, or some combination. Either way, it equates to more air = more power. In terms of our cars, it basically means, the colder the air entering the turbo, the faster it will spool and you'll get more power for a given boost pressure.

 

Because when you have high humidity the air being draw into the turbo has less molecules of O2 due to the water displacement.

When you use water injection you squirt the water in during the combustion cycle after the air has been through the IC and piping. This has the effect of cooling the air/fuel mixture and compressing the already available O2 molecules even more for a larger bang.

 

You don't gain molecules of air, you make the ones you have closer together (denser). Think of it like a bunch of springs in your hand. Compress them slightly and they do not expand very fast. Now compress them tightly (cold air) and when you let go they go shooting everywhere. This process works in combustion. The denser the O2 (more tightly packed) the faster they will expand when the combustion cycle takes place. This has the effect of giving you a more powerful ignition which in turns pushes harder on the piston.

By restricting the flow of air through the pipe you will decrease the pressure of that air but increase its velocity. This is explained by Bernoulli's Principle. In effect the air is moving at a constant rate of flow. If you constrict part of the path the same volume of air must move through that restriction. The only way to do that is increase the velocity of the air which inversely decreases the pressure.

 

AAAhhh!!