Engine Tech: Thermo-Dynamics Behind Cold Air Intakes

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spiffyguido
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Engine Tech: Thermo-Dynamics Behind Cold Air Intakes

Postby spiffyguido » Thu Feb 01, 2007 2:22 pm

The quest for more horsepower is a never-ending one for those of us who want to constantly improve the performance of our vehicles. As a long time fan of Honda automobiles, I, like you, certainly have noticed the entrance of cold air intakes into our vocabularies and the subsequent rise in their popularity. Experienced tuners and junior noob sauces alike, everyone seems to know about cold air intakes, but do we understand them?

There's little question why Cold Air Intakes have enjoyed such rampart popularity. As a potential engine performance improvement, they're a dream. Cold Air Intakes are generally easy to install, inexpensive, require no serious vehicle alterations to be made and often promise reasonable performance gains.

The performance increases associated with Cold Air Intakes vary a great deal, and many outrageous claims have been made about the gains that can be realized. When it comes right down to it though, it's not the numbers that should be of concern to you, but rather the concept and science behind it.

First off, it's probably a good idea that we ask ourselves, "so what's the big deal about cold air anyway?". Many people incorrectly believe that it is the temperature of the air that makes the difference. This, however, is only partly true; it's actually the density of the air that makes the difference. The temperature of the air is mostly important because lowering the temperature of the air increases its density. This higher density air has an impact on engine performance because for a given volume there is more combustible oxygen available as density is raised.

With a simple experiment, it is easy to see how temperature has an effect on air. If you blow up a balloon at room temperature and then put it in the freezer, it will shrink substantially. The air in the cold balloon has higher density than the warm balloon and lower volume.

Now, imagine that you had 6 balloons filled with the same amount of warm air. All of these balloons would have the same volume and the same density. Next, imagine that you put 4 of these balloons in a freezer and cooled them sufficiently to reduce their volume to half of what it was originally.

Finally, imagine that you have an engine that consumes 2 warm balloons of air for each intake stroke. Since the volume of cold balloons is half that of the warm balloons it follows that the same engine would consume 4 cold balloons of air for each intake stroke.

Recall that all six balloons started out the same, and all we had to do to provide our engine with twice as much air was lower the temperature of the air. Although the values that I used in the balloon example are far outside the realm of what can be done with a Cold Air Intake, it does show use the science behind what is happening. The high density air provided by any functional Cold Air Intake system provides the engine with more air to aid combustion. This ultimately results in better combustion and more power.

Unfortunately, it's not terribly easy to find cooler air underneath the bonnet of a car. The engine bar is a warm place; it doesn't take long for a hot engine to warm the air around it. The challenge then is to pope the Cold Air Intake to a location where there is cold air. In this regard, every car is different. If you choose to acquire a Cold Air Intake for your car, put some thought into where you will draw air from.

The cooler air is not the only reason that a Cold Air Intake can help you make more power. Most Cold Air Intakes also improve the ease of air flow into the engine over the stock system. This is helpful. A stock intake hose set is often full of bends, curves and twists. Stock piping is often too narrow and may even be made out of ribbed piping. All of these are detrimental to the efficiency of air flow into the engine.

Ultimately, increasing the efficiency of the intake will increase the engine's volumetric efficiency. Volumetric Efficiency is defined as the percentage of intake charge that an engine takes in when compared to the theoretical maximum it could take in during an intake stroke. Maximizing this percentage will always help you out.

If you install an intake that allows for easier flow and supplies a cooler supply of air, extra torque (and therefore horsepower) is yours for the taking. Don't expect a Cold Air Intake to work miracles for you, but do expect it to help a little. As any experienced tuner will tell you, performance is built half a horsepower at a time. Engine tuning really is a nickel and dime hobby; you focus on many small changes to make a big difference.

Have fun out there, and drive safely.


Copyright Notice: This original article was written for PreludeDriver.com. Reproduction without prior written consent is prohibited.

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RedRacer
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Postby RedRacer » Fri Feb 02, 2007 3:08 am

Very good article Spiff.

Absolutely true.


Cold air = dense air.

Dense air = oxygen rich.

Oxygen rich = happy intake system.

(just remember kids, if you poke that intake through and down, make sure you have a valve to prevent snorkeling of water into the intake on those deep water days)

Water in intake = NOT GOOD.

si96lude
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Re: Engine Tech: Thermo-Dynamics Behind Cold Air Intakes

Postby si96lude » Fri Feb 04, 2011 8:32 pm

I know that AEM has 3 intakes for my 96 si with the H23. Short ram(nah) Cold Air(probaly) and dual chamber(I do not know what the benefit of this one is) Any thoughts? Comparrisons with other brands?

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spiffyguido
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Re: Engine Tech: Thermo-Dynamics Behind Cold Air Intakes

Postby spiffyguido » Mon Feb 07, 2011 1:21 pm

No direct experience with any of them on Preludes, sadly. AEM in general makes very good stuff, so you can count on quality being high. I've helped install the cold air system on a Sentra before, and it seemed to help the car a bit. I don't know anything about the dual chamber one. Check the AEM website for dyno charts.




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