I did my fair of searching but still dont understand it. I know/ or at least I believe it to be true that for turbo charger applications, colder air is better. Cold air increases boost while hot air keeps the boost stock or a little down. Can someone please explain why this is true/false?

 

true...cold air is more dense

more dense = more air

try googling it or howstuffworks.com

 

Cold air more dense = more power,hot air less power=true.

 

I tried googling it and didnt find much. Also searched here and other websites

 

The biggest factors in turbo efficiency is temperature and density. It's true that colder air is denser than warmer air but altitude and current weather conditions play a big factor. You'll also notice that as humidity goes up your peformance suffers due to water displacing air.

You will find that the most power will be during colder air temps and higher barometric pressures.

 

so is that it. cold air is more dense so it lets more air in which means more power?

 

It's all explained in chemistry book too

 

PV=nRT

 

In laymans terms yes. But like I said, other factors such as barometric pressure, humidity and altitude all factor in on how effecient the turbo is. Cold air does not "Let" more air in per se. If you take two seperate cubic centimeters of air (just imagine it) and have one at 60 degrees F and the other at 100, the colder one will have more molecules of O2 in it.

Nitrous Oxide is a good performance adder because of this. When it is compressed it breaks down the chemical chain and releases the oxygen creating a denser O2 charge. Add that with more fuel and you get more bang.

 

yep, it is all about density! That's why the biggest intercooler you have, the best performance you get. I preefer to add a air/water intercooler that easily fit than XS front intercooler. if you want high boost, go to water injection!

 

Your reasoning is flawed. As intercoolers get larger they take longer for the air to pass through causing a pressure drop on the output side. This has the negative effect of lowering boost pressure coming into the engine. So therefor bigger is not always better.

Air to water IC's work well when you can keep the water colder than the atmosphere. Otherwise the water will heat soak just as bad, if not worse than an air/air IC.

 

I've often thought about this and want to offer a different idea. If the intercooler is so large that it actually works as designed (cools the air), wouldn't it make sense that when the air comes into the hot side, it is expanded to a certain number psi, and as it travels through the IC, the air gets cool causing it to become less dense, and that therefore causes the psi drop. If this is true, couldn't we just reduce the size of the exit by say 1/4" to compensate for the psi loss?

 

Damn, now where is my thermodynamic principles book when I need it!

I'll try to explain this without getting too technical. As you compress air (turbo etc) it heats up. This heated air obviously is no good for combustion as it's not very dense in molecules of O2 and can cause pre-ignition. You would like to have the coolest air possible in the cylinder because the hotter the air is the less it will expand when combustion takes place.

So we put on a radiator of sorts called an intercooler. This object (if designed correctly) will take the hot compressed air and cool it through convection. The pressure does not change much as long as the restriction of the IC is minimized. So if your turbo puts out 19 psi of hot air, the IC should put out 19 psi of cooler/denser air. Oxygen density is not directly related to pressure. If you have 1 psi of hot air or 1 psi of cold air it's still 1 psi. But the cooler air will have a denser O2 level.

For the last part of your question, restricting the outlet of the IC will cause the velocity to go up but pressure to drop.

 

evos love cold air

 

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This is where I get confused. An increase in humidity means that there is more moisture in the air, right? More moisture is another way of saying more water. If more moisture in the air hurts performance, then why would water injection increase performance?