What do CAI's REALLY do?

canuckz71

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Saw this on another forum, seems to provide some insight into what many people believe to be true.

The following is something I wrote a while back, and a friend suggested that I post it here to get some feedback on it. Please comment with any agreement or disagreement on what is stated. If I am missing something on this, I certainly want to know about it. Thanks in advance!

---Read below---

Have you purchased a cold air intake kit for your vehicle yet? If so, you are among the many thousands who (for various reasons) have bought into this technology. But does it really do what you thought it would?
The most common reasons people give for installing a Cold Air Intake are:
1.More Horsepower
2.Better Fuel Efficiency

More Horsepower! Now this one is true, but might be a little misleading. Cold air intakes can result in actual gains in power, but not necessarily in the way most people are expecting them. The key that is typically missing in the mind of the average consumer is that the only time power is increased is when the engine is at Wide Open Throttle (WOT). For those who don't know what that means, WOT is basically when the gas pedal is pressed all the way to the floor.

Some are now thinking "Wait a minute! The cold air intake lets cooler, more dense air into the engine. It also has less restriction than the stock setup. This lets it 'breathe' better, and therefore is more efficient." What can I say? You're right...at wide open throttle. What many people don't realize and what many others simply forget to consider is that there is a throttle valve connected to your gas pedal that is constantly restricting the air flow into the engine. The only time it is not restricting the airflow is when it is wide open...hence the term WOT. Some will now say "But it will still breathe more efficiently even at part throttle." You must then remember why there is a throttle valve in the intake to begin with. The throttle valve determines how much air enters the engine, and the engine computer (for fuel injected engines) determines how much fuel to mix with the air. Several factors influence how the computer determines this, but the result is basically the same: a fixed Air/Fuel Ratio will be supplied to the cylinders. This should be obvious since all modern vehicles have to comply with EPA emissions standards.

That means that more air = more fuel = more power = more speed. Now that's good if you're at WOT, but how many of you drive at WOT even 1% of the time? The fact is that you almost always drive in part throttle...because you're usually limiting the vehicle's acceleration. That is the key. Any time you limit vehicle's speed/acceleration with the gas pedal, you are actually limiting (restricting) the amount of air entering the engine. This defeats the purpose of the cold air intake, high-flow intake, high-flow filter, etc. It is only effective when you're at WOT.

One thing should be clarified here...when I refer to WOT, that can also be a little misleading. The condition where these devices increase power is not always exactly at WOT. The throttle valve on a car's intake system is typically a butterfly valve. The more it is closed, the more restrictive it becomes. The least restrictive condition is when it is wide open. Keep in mind that the intake system is sized to operate the engine through a full range of speeds and load conditions. If you get full power from your engine at 5,000 rpm, the throttle valve is sized allow air to flow through it at that speed. Now how much air do you suppose is flowing when you're only turning the engine at 2,500 rpm? This is the situation you have when your're pulling a heavy load (trailer, etc.) in a high gear. This is the situation I find myself in with my pickup when pulling a travel trailer. In 3rd gear at 60 mph, the intake manifold pressure and mass airflow don't change at all from about 70% open throttle to 100%. Why? The throttle valve is effectively at WOT for that speed. There is no measurable resistance being offered by the valve when at 70% open. Does that mean that a cold air intake would help when towing heavy loads? Probably not. The reason is that when you have the condition described above (you have more pedal, but it doesn't change anything), the intake system (filter & piping) is providing very little air resistance. You know this because the primary form of resistance--the throttle valve--isn't even doing anything from ~70% and up. That tells you that there is not as much air flowing through the intake as there would be at high rpm (like if you down-shifted), and therefore your air filter creates a very small amount of resistance by comparison. NOTE: This is assuming that the air filter is clean. If it is clogged up, that's a different story.

In summary, the cold air intakes and high-performance filters are good for improving full-pedal engine power. Practically that means that you are buying a modification that helps you pass (at full-pedal) or race. Don't expect fuel economy gains...sorry.
 

Zembonez

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Basically, they make more noise.
 

mr_bots

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Basically, they make more noise.

:werd:

The only benefit is that they remove the resonators so the flow is a little smoother and louder. The cooler, denser air is BS though. How is it cooler and denser when it's pulling it in from the exact same hole in the fender that the stock air box was? In some cases they can even increase IATs as a lot of aftermarket intakes are metal because it looks cool but metal will conduct more heat off the engine than plastic thereby heating up the air going through it on it's way to the engine.
 

Zembonez

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OEM air filter housings are designed to flow well beyond what the engine needs. They are probably that way because a restriction at high rpm might wreak havoc on the emissions.

It is possible that the smoother airflow of an aftermarket system would create a tiny bit of added power at high rpm under WOT.

I seriously think most of the "added power" people claim to get from them is inside their head. They equate noise with more power.
 

Zembonez

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They do sound good on some engines!
 

tleach17

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Mine did add some great sound on acceleration. :thumbs: But I felt a definite increase in low end torque. I noticed right away that the truck did not down shift as early climbing hills. When towing it shifted less under light acceleration. Anyone can say what they want but I know my truck and I got better performance out of mine and I have no reason to lie about that.
 

mr_bots

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Also :werd:

LS engines sound pretty good with intakes and exhausts. Don't count on me throwing either on my Jeep though as I'm not a big fan of the sounds V6s make un-muffled.
 

buckshot85

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They are good for messing up your mass air flow sensor.. went through 3 of them :facepalm:
 

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