What Do Cold Air Intakes REALLY Do?

Discussion in 'Performance & Fuel' started by 99'HEARTBEAT, Feb 19, 2014.


    99'HEARTBEAT MODERATOR Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    There has Always been a Debate, and/or some Discussion's here on the Site, regarding Aftermarket Cold Air Intake Systems, Do they Do what the Aftermarket Company's Claim they Do....."Increased H.P. and/or Improve Fuel Mileage"

    The Information below is from a Member, On One of the Other Chevy/GM Truck Forums, and the Title of His Thread Was "What Do Cold Air Intakes REALLY Do?"......I found this Information to be Very Interesting, with Some Strong Points to it.

    I'm Not Asking Anyone to Agree or Dis-Agree with this Information, You Guys Read it, and Come-Up with your Own Conclusion's.

    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.
    ChevyFan and McClintoc like this.
  2. ajarman

    ajarman Epic Member 5+ Years ROTM Winner 1000 Posts

    This needs to be a sticky!
  3. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    this is very well said. I happen to agree with him.
  4. JimmyA

    JimmyA Rockstar 4 Years 100 Posts

    NUFF said!!!!!!!!!!
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Nice piece Mike.
    Most intake systems do more for looks than any performance gains, If I couldve found an inexpensive less maintenance intensive drop in filter I never wouldve installed my new intake system

    99'HEARTBEAT MODERATOR Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    Thanks Tim....I Felt this Piece was Worth Posting-Up, and Today was Good as Any.
  7. TimmyG

    TimmyG New Member

    I did it for the sound
  8. TomsHHR

    TomsHHR Rockstar ROTM Winner 100 Posts

    My thought is that it finishes filling up the engine compartment with stylish plastic that gives the impression that it works.

    Yep, Steve I still hang around.
  9. dobey

    dobey Epic Member 5+ Years 500 Posts

    The main problem is that most people assume the factory system is somehow not a cold air intake, because all of these things are sold as CAI (even when many of them are in fact, not cold air intakes).

    Also, pedal to the floor no longer means 100% throttle opening. With modern engines that have electronic throttle control, the blade position is totally controlled by the ECM. How hard you press the gas pedal is only one of many variables that determine what the position should be.

    There are some other things in the post, which, while being very common, are not necessarily always true. On any 2002+ GM truck, if your only mod is a CAI kit, the most common and only truly perceivable improvement you're going to get, is a better intake sound. Worst case, you'll install one of the "kits" that is actually a hot air intake, and have a slight loss in performance. The factory setup is a cold air system, and it's designed to meet certain government regulations, including noise level requirements.

    One thing in particular, more fuel being consumed does not necessiarly mean that you will have worse MPG, and it can mean you do get better MPG. It depends on a lot more variables than simply "the ECM threw more fuel at the engine" to determine efficiency. If that additional fuel is only added at 5000+ RPM, and you only ever go up to 4000 RPM, you will never see that additional fuel consumption. If a tiny bit is added at 1000-1200 RPM, and you make a bit more torque in the low end as a result of denser air and a tiny bit more fuel used in that range under load, you may still see a slight MPG increase in city traffic, as you are making more power in the range you need to get the 6000 lbs truck moving, which means you'll get moving faster, and up into the 2000 RPM range and higher gears more quickly. That can actually result in a slight MPG improvement.

    There are way too many variables to make blanket statements like "they are worthless and not worth the money" or that they "only work at WOT," which is not necessarily true either. What is a valid blanket statement to make though, is that CAI kits are primarily a supporting mod, and not power adders. If you've got a cam, head work, exhaust, a turbo, and maybe an aftermarket intake manifold too, you will see much more benefit to a CAI in the power department.
    azrwilkinson likes this.
  10. benoit230

    benoit230 Member

    Very informative and interesting. I have a cai on my Ford Focus and after reading this I have to say - I do only feel the gains at WOT. I did quite a bit of research on it but never ran into this information. I do like the sound though as well so I guess it's not all bad.

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