CAI; AEM or K & N
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This is a discussion on CAI; AEM or K & N within the New Member Hangout forums, part of the Community - Meet other Enthusiasts category; I have a 2010 wrx and I'm staring to do some mods; I want to start with a CAI but ...

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    CAI; AEM or K & N

    I have a 2010 wrx and I'm staring to do some mods; I want to start with a CAI but I'm not sure which one to go with. K & N or AEM? AEM claims per dyno report that it will gain 36hp at 5300rpm and k & n claims only 14.28hp at 5228rpm. Can you guys help me out.
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    zax
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    Neither. Keep the intake stock. The stock intake for the WRX has proven not to be restrictive.

    CAI are essentially a worthless mod for a turbo'd car since the intake charge is drastically heated by the turbocharger anyhow. If you want lower piston charge temperatures, buy an upgraded intercooler and a tune.

    Plus an AM intake without air straightners will throw off your MAF readings. You may run a dangerously lean condition or rich condition that fouls your spark plugs and O2 sensor.


    keep it stock. If you want the sound, perform the "elbow silencer delete" mod. The best "first mod" is almost always an EM system since you will use it for any future mods. Cobb or TurboXS UTEC offer excellent Engine Management systems. Remember, NEVER mod the engine without a tune.
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    Quote Originally Posted by zax View Post
    CAI are essentially a worthless mod for a turbo'd car since the intake charge is drastically heated by the turbocharger anyhow. If you want lower piston charge temperatures, buy an upgraded intercooler and a tune.

    Plus an AM intake without air straightners will throw off your MAF readings. You may run a dangerously lean condition or rich condition that fouls your spark plugs and O2 sensor.

    Both of these statements are wrong.

    Temperature: If this were the case, then why do turbocharged cars take better to 60 outside temps than 100 temps? Yes, the turbo will heat up the air, but if you have a lower temperature at the start of the intake tract you will have a lower one at the end of it as well.

    MAF readings: You don't need air straighteners, and nor do all intakes throw off readings too much. Both of the ones he mentioned are generally considered fine to run without tuning.
    Last edited by brfatal; 03-11-2010 at 08:02 AM.

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    Quote Originally Posted by brfatal View Post

    Temperature: If this were the case, then why do turbocharged cars take better to 60 outside temps than 100 temps? Yes, the turbo will heat up the air, but if you have a lower temperature at the start of the intake tract you will have a lower one at the end of it as well.
    Maybe. But how much of a difference is 30 degrees F ambient temp going to make on power numbers if your post-turbo temps are raised by over 190 degrees F? You're still constrained by the air-air intercooler heat bleed. A turbo'd car that does track runs @ 60 degree temps will have 60 degree air flowing through the intercooler and better heat flow properties than one that runs at 100 degrees ambient. I'm not saying that there are no gains, as clearly cooler intake charge will slightly increase the density of air in the cylinders, but I highly doubt that the benefits are going to be as great with a WRX as they are with a N/A Honda Civic.

    Quote Originally Posted by brfatal View Post
    MAF readings: You don't need air straighteners, and nor do all intakes throw off readings too much. Both of the ones he mentioned are generally considered fine to run without tuning.
    On stock perhaps. My buddy ran an Cobb Stage 1 map (v. 1.0) on his 2002 wrx sedan with a Fujita CAI and it ran like hell: idled like hell, noticeable performance decrease, drastic fuel economy decrease on the order of 10 MPG city 13 MPG highway. So he swapped in an AEM CAI and same thing occurred. He reverted to the stock airbox and everything went back to normal
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    Your stock intake draws cool air already. My IAT's are always near or at ambient temperatures, even when parked they only climb a few degrees. Start moving and things are ambient again.

    There likely is a small hp increase at that rpm range, but not a worthwhile amount. If it were torque at 3000 rpm, then I'd take it.
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    Justin prompted me to do a little study about intake temperatures just to satisfy my own curiousity.

    Suppose we take the ambient temperature to be 30 degrees F (Tenv).

    The initial intake temp registered by the MAF for the stock intake box may be 70 degrees F.

    The initial intake temp registered by the MAF for the CAI may be 40 degrees F.

    In a perfect scenario, the intake charge will undergo 3 temperature stages:
    1. initial intake temp (T0)
    2. Temperature post-turbocharger (Tb)
    3. Temperature into the cylinders (Tc)
    and we'll stop there (pretend that there is no excess heat from internal combustion)

    In this perfect scenario, the intake charge undergoes an adiabatic compression by the turbocharger. This heats the incoming air by the same amount no matter the intial intake temp. To be reasonable, let's call this 190 degrees F.

    Now Tb = 230 F for the CAI and Tb = 260 F for the stock airbox

    The intake charge will now enter the intercooler where it will dwell for some time. When air is flowing through the intercooler, it will undergo forced convection cooling. The equation for this cooling is

    T(t) = Tenv + (T0-Tenv)exp(-rt) where t = duration of cooling and r is a constant that depends on the fluid dynamics and area of interface between the two heat-exchanging materials (intercooler size). For our purposes, we will take r*t=1 but we could calculate this in practice by taking the air consumption of the engine and size of the intercooler into account.

    So for our study, Tc = 103.5759 degrees F for the CAI and Tc = 114.6123 degrees F for the stock airbox.

    So, even though we started with a 30 degree F intake charge temp. difference, we only ended with an 11 degree F difference when the intake charge enters the cylinders. So the CAI will make difference, albeit somewhat less than with a N/A car.

    EDIT:
    If we increase the area of the Intercooler by 33% (in perfect scenario) for the stock airbox setup, Tc drops to 90.829 degrees F, which is less than the CAI with stock intercooler
    Last edited by zax; 03-11-2010 at 12:32 PM.
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    Quote Originally Posted by zax View Post
    Neither. Keep the intake stock. The stock intake for the WRX has proven not to be restrictive.
    Untill you hit a certain power level. Your being to generalized and giving incomplete information. The biggest restriction is filter size. Next would be the inlet hole size of the airbox.

    Quote Originally Posted by zax View Post
    CAI are essentially a worthless mod for a turbo'd car since the intake charge is drastically heated by the turbocharger anyhow. If you want lower piston charge temperatures, buy an upgraded intercooler and a tune.
    The IAT sensor is placed in the MAF. Its reading are just as important as the MAF so when it is time to upgrade to an intake while still using the MAF sensor I would most certainly use a CAI. It not that the colder is air going to give me more power but it will insure that the IAT and MAF sees the lowest temps possible. Once again your being to generalized. If you want to say its not the best mod for a stock vehicle,fine,but you didn't. Oh and the stock intake is a CAI...........
    Quote Originally Posted by zax View Post
    Plus an AM intake without air straightners will throw off your MAF readings.
    Not true. Just because it doesn't have air straighteners doesn't mean the intake will have turbulence. Its all in the design.

    Quote Originally Posted by zax View Post
    If you want the sound, perform the "elbow silencer delete" mod.
    He has a 2010. There is no "elbow". The 2008+ use the Legacy GT type airbox.
    Last edited by Donkey; 03-11-2010 at 09:30 AM.
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    Quote Originally Posted by zax View Post
    keep it stock. If you want the sound, perform the "elbow silencer delete" mod. The best "first mod" is almost always an EM system since you will use it for any future mods. Cobb or TurboXS UTEC offer excellent Engine Management systems. Remember, NEVER mod the engine without a tune.
    There is no elbow silencer delete for the newer WRXs.

    Silly engineers with their technical equations. A much more realistic way to test something like this is a basic experiment where you have a control and treatment, do a number of runs on a dyno of each, and let the law of large numbers do its work (I'll spare you the proof ). Just my statistician $0.02...

    OP: Sorry but this is a topic that comes up a lot and the best advice I can give is never to believe manufacturer's claims of power gains.

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    LOL Ron is cleaning up my mess. Yeah you're probably right that I left out some necessary information.

    To OP, I should correct myself by saying that IMO CAI are an unnecessary mod for a stock WRX. There are a lot better things out there to spend your money on for the time being. EM may give you 20-30 WHP for even an OTS map, plus give you a platform to work with future mods. But it is true that SOME CAI and SRI will fool the MAF, so you have to be somewhat careful in choosing the brand.

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    Quote Originally Posted by zax View Post
    LOL Ron is cleaning up my mess. Yeah you're probably right that I left out some necessary information.

    To OP, I should correct myself by saying that IMO CAI are an unnecessary mod for a stock WRX. There are a lot better things out there to spend your money on for the time being. EM may give you 20-30 WHP for even an OTS map, plus give you a platform to work with future mods. But it is true that SOME CAI and SRI will fool the MAF, so you have to be somewhat careful in choosing the brand.

    @ Ron -- Did I redeem myself?

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    Quote Originally Posted by zax View Post
    LOL Ron is cleaning up my mess. Yeah you're probably right that I left out some necessary information.

    To OP, I should correct myself by saying that IMO CAI are an unnecessary mod for a stock WRX. There are a lot better things out there to spend your money on for the time being. EM may give you 20-30 WHP for even an OTS map, plus give you a platform to work with future mods. But it is true that SOME CAI and SRI will fool the MAF, so you have to be somewhat careful in choosing the brand.

    @ Ron -- Did I redeem myself?
    Much better. Keeping the information consistent helps people when they actually do try to search or read the thread.
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    i've just put a AEM cold air on my wrx which made a world of difference in power and sound aswell but now i've got to leave my MAF sensor unplugged which i do not like cause obviously its there for a reason, but ya my car will absolutely not run with it plugged in. i've noticed my gas mileage went down the drain, im only putting like tops 175 miles to a tank which is mostly highway driving. Is there a real danger of ruining the car with it unplugged?? and what are the dangers?

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    Quote Originally Posted by 2005_silver_wrx View Post
    i've just put a AEM cold air on my wrx which made a world of difference in power and sound aswell but now i've got to leave my MAF sensor unplugged which i do not like cause obviously its there for a reason, but ya my car will absolutely not run with it plugged in. i've noticed my gas mileage went down the drain, im only putting like tops 175 miles to a tank which is mostly highway driving. Is there a real danger of ruining the car with it unplugged?? and what are the dangers?
    Uh, honestly you're not in a place to make a proper judgement. I'd get that taken car of, soon. You probably have a bad/dirty sensor.

    And no, it will not make a noticeable difference in power. It's all in your head.
    Last edited by brfatal; 03-11-2010 at 07:45 PM.

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    Quote Originally Posted by 2005_silver_wrx View Post
    i've just put a AEM cold air on my wrx which made a world of difference in power and sound aswell but now i've got to leave my MAF sensor unplugged which i do not like cause obviously its there for a reason, but ya my car will absolutely not run with it plugged in. i've noticed my gas mileage went down the drain, im only putting like tops 175 miles to a tank which is mostly highway driving. Is there a real danger of ruining the car with it unplugged?? and what are the dangers?
    Right...cold air intake makes a difference in power without a tune and with the MAF unplugged...yeah, you'll go far that way.

    Before you go offering advice to people you should work on getting your issues figured out. Your car is effectively running in limp mode using only the MAP sensor for fueling, which is why it's running so rich. You're not even seeing stock numbers, yet you claim to have noticed a performance increase with a CAI? Your butt dyno must be completely out of whack.
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    Quote Originally Posted by brfatal View Post
    And no, it will not make a noticeable difference in power. It's all in your head.
    The power of the mind

    "deez AEM stickaz add like 10 horsepowa each!!!"
    If I had a dollar for every Civic driver who thought that, I wouldn't be driving a WRX.
    Last edited by zax; 03-12-2010 at 05:49 AM.
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