If intercoolers compact more air into a square inch....isn't it logical for PSI to increase throught the intercooler?

Because cold air is more dense....thus more compressed...right?

sounds correct to me... but the i\c helps free up psi.. with a intercooler you can boost more..


1

Well, an I/C cools the air, but when it passes through the fins there is actually a pressure drop because it slows the air down. So I'm not sure about it creating more pressure, all I know is that it comes out the other end of the I/C less pressurized. So the answer to your question is no, but I'm not sure why.

Well if it slowed down...wouldn't preasure build up...causing a psi increase?

Well if it slowed down...wouldn't preasure build up...causing a psi increase?
Now this I can answer with an example - Think of a tire on your car. If you put more weight in your car it doesn't change the pressure of the tire. Again I'm not sure why, I just know it doesn't.

The point of the turbo isnt to add compression, its just to put more air into the engine, so it really dosent matter.

Your tire example wouldent work. When you put more weight in the car, the air goes to the top of the tire. Unless your intercooler bulges out, this example wouldent work.

I would have to think that the compression would lower, because cold air takes up less space, but then the turbo would continue to pump in more air to keep the pressure uniform, so it probably stays the same... :banghead: My head hurts...

im not too sure on the specifics of intercoolers but...

there is no pressure change in an ideal cooler, as temperature decreases the density will increase, this is good, the more O2 molecules that go in the engine the more fuel you can burn

the idea of turbos and all that is to increase the density of air, dont get hung up on the idea of pressure

the idea of turbos and all that is to increase the density of air, dont get hung up on the idea of pressure
Take the complete opposite of what you said and thats the right answer. The purpose of an intercooler is to increase density of the air.
Purpose of a turbo is to put more pressurized air into the engine, hence the PSI rating on a turbo car. Like I am running 9 PSI in my Daytona, that is pressure not density.

LOL, PWMAN beat me to it.

A turbo is specifically meant to force more pressure into each cylinder raising the compression. That is why you can't add a turbo to a high compression engine without changing the compression first.

Anyhow, the deal with an intercooler is that they are big and they have to be filled with air. You can expect about 1.5 PSI at the most. Any intercooler that allows for more of a pressure drop isn't worth your money. It all depends on how they are designed. The reason the intercooler allows you to run more boost is because it cools the intake charge. If you didn't you would get detonation. It is not that it "frees" up more boost. It is that it cools the air enough to keep it from causing detonation. Also, colder air means more power, it is also improves responsiveness and will allow the turbo to fill the cylinders quicker.

i dont see how thats the opposite of what i said, its the same thing

you repeated what i said about intercoolers increasing density

a pressure increase from a turbo, is also a density increase (assuming constant temperature),you want more molecules of oxygen to burn more fuel, higher density is key

you can talk all you want about pressure ratings but that doesnt accurately desrcibe the situation. there can be an infite amounts of different densitys at a given pressure, depending upon temperature

i was just trying to explain the basic thermodynamics, but i guess im getting to scientific :banghead:

a pressure increase from a turbo, is also a density increase (assuming constant temperature),you want more molecules of oxygen to burn more fuel, higher density is key


No it isn't. Density stays the same. A turbo forces more air (of the same density) into the engine. When you add more fuel to compensate for more air you get more power. The intercooler is the only thing that changes the density. That is why you have to have lower compression in a turbo car, because the compressed air actually causes less density and higher temperatures. That is also why when you add an intercooler you can run more boost, because it gives the incoming air more density.
Yes higher density is important, thats why there is such thing as an intercooler! The turbo itself does not change the density.

honestly i dont know that much about turbos, but i do know thermo, and thats basically what were talking about, so maybe im wrong, but hear me out

inside a cylinder just before ignition there is a fixed volume. you say a turbo put its "more" air in, i assume you mean the turbo is pushing a higher volume of air in? :eek7: but this isnt possible because the cylinder can only hold a certain volume of air, turbo or not. the air is at a higher pressure and therefore a higher density in order to burn more fuel, does that make sense?

Higher pressure does not mean higher density.

i know man, i already said that

the air is at a higher pressure and therefore a higher density
Than what is that?

I also must add that turbos run VERY hot so they pump out ait that isn't very dense until you get the intercooler to cool that intake charge. Remember that the hot exhaust gasses combined with the fact that the turbine spins at over 100,000 RPM turbos can get pretty hot.

We all know that hot air is less dense.

I also must add that turbos run VERY hot so they pump out ait that isn't very dense until you get the intercooler to cool that intake charge. Remember that the hot exhaust gasses combined with the fact that the turbine spins at over 100,000 RPM turbos can get pretty hot.

We all know that hot air is less dense.
Yeah that's what I was trying to say earlier. Boiles Gas Law states that if a gas is compressed it heats up-which is what a turbo does. And ''we all know that hot air is less dense''. :bigthumb: You took the words right out of my mouth.

I agree with you, but I'm going to try to clarify for our younger readers.

An intake manifold of compressed air, say 15psi boost, holds twice the volume of the manifold, of molecules of air at atmospheric pressure, so they are more dense, or closer together. When they were compressed, they vibrate, which releases heat energy. Most of the heat comes from compressing these molecules closer together. When the intake valve opens, they try to expand as they rush into an empty engine cylinder, allowing expansion until the cylinder reaches 15 psi or the intake valve closes. And I'm going to tell you that the average street engine will never see 15 psi in the cylinder before the valve closes. There just isn't enough time or head flow. When you cool those vibrating molecules down in an intercooler, they expand at a slower rate as they enter that empty engine cylinder, so you end up with more molecules of air in the cylinder. So you can burn more fuel and make more power. You have also raised the detonation threshold, so you can run a few pounds more boost. But that is another story.

Here we go, Finally something I understand. When you compress air in the turbo or supercharger, it gets hot due to compression and from the compressor being hot itself. This makes it not very dense in and of itself (although offset by the pressure its at), and as it passes though the intercooler, it cools down (obviously) and becomes more dense. Thus the same amount of air (when more dense) takes up less space (which is the entire reason of wanting cold air; so you can pack more in); now ask yourself, what is pressure really? Is pounds per square inch, or kg/cm^3. And you ask yourself, so why does an intercooler drop the pressure that the manifold see's? Partially becauase its agitaiting the air and forcing it to move quickly (whitch we know decreases pressure. The same reason that your car moves when someone passes you at a stop light, the quickly moving air creates a low pressure zone, sucking you twards each other).
Thats part of it, and the other part comes from - since the air is more dense after being cooled, the definition of pressure tells you that the pressure will decrease. Pressure is, more or less, a measure of force due to the air being compressed and wanting to cross to a lower pressure area. Now if the volume of air in a certain area decreases, pressure decreses(and the way the volume changes in a sealed enviroment is temperature, which effects density). Think of this example, your tires have more pressure in them after youve driven (heated them up) than if they sat in the cold overnight, without adding or subtracting any air. So the fact that the intercooler- cools, decreases the pressure. That is why there are "low pressure drop" intercoolers, but never a "no pressure drop" intercooler. They are decreasing the effect of the inperfections of the metal and contruction, but they cannot change the properties of air. So your probably saying, well if the pressure decreases, and pressure = power, then why do we want an intercooler? Well the entire reason you cant pressurize over a certain PSI, is becuase the heat buildup causes predetonation, so without an intercooler, the highest pressure you can acheive is less than with an intercooler, becuase the air will be too hot, even with the pressure drop incuded.

I noticed that earlier there were bits an peices of this argument but noone had put it all together in a form that people would agree upon, so I thought I would.

Here you go sweedishfish, I've got some time so I'm gonna help you out too. I notced your question about the dynamics of the turbo, and here we go. The turbo pressurizes the air to some ATM > 1 (1 ATM is atmospheric(outside) pressure (give or take)).
So in a normally asperated engine, when the piston sucks in air, its sucking it in at 1ATM. So the most air you could possibly fit in there is the volume of air that equates to 1 ATM per the volume of the cylinder (I dont know exactly what that is, it would depend on alot of things).
But say now you pressurize the intake to 8psi, now you have effectively increased the "ATM" that the cylinder see's. So now the ATM is higher and the most air you could possibly fit in there is the volume of air that equates to (some greater) ATM per the volume of the cylinder; which equates into more air in the cylinder. And since it is pressurized the greater change in pressure between the cylinder (approx 1-2ATM from the exaust stroke) and the intake, forces more air in, faster.

Be it that alot of the numbers are estimates and guesses, but this is not a mathmatical approach, so I don't care. And if you don't understand this, its useless to throw a bunch of numbers around that will confuse you more. Which is why I gave all the examples, to help you understand.

Hope this helps,
Buzz1167
Jon N