Can anyone explain why the AEM CAI.........

You're right, but you have to look at it from a point of flow (in and out). Your engine is essentially a big air/fuel processor- the more of it you can move in and out, the faster it runs and hopefully the more power it makes. You can make all the intake and fuel mods you want (or exhaust), but if you improve one while not improving the other you aren't going to realize the full potential of *any* of those mods.

The dynamics of it are explained easily for intake and exhaust; a smaller & longer pipe typically yields improved low-end torque while a larger, shorter pipe yields better high-end power. That's just the simple fact of it.

By improving the intake you're not "pushing" anything more into the engine- the engine is *sucking* through the intake, just like you would through a straw. Doesn't matter how hard you suck, if the straw is the size of a pinhole, it will be restrictive. Likewise if the straw is the size of a sewer pipe but your dog w/no lips is on the other end trying to suck (and can't), you won't move any air (think of that as a big intake and a restrictive exhaust).

<font face="Verdana, Arial" size="2">what u said about H/E is correct due to higher flow of EG's and therefore changing the backpressure. But how does the CAI have anything to do w/backpressure. [/B]</font>

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As Billy stated the other day, and I will reiterate, backpressure is not the major detriment to exhaust gas flow. Exhaust gas velocity is the single most important aspect of exhaust gas flow.

Now the reason the AEM supposedly looses low end torque is due to greater airflow at a lower velocity. The valves only stay open for a certain amount of time and if the velocity of the incoming air is less than it was with the stock intake there is not as much air in the chamber to be used for combustion. This leads to a loss of low end torque.

Personally, my low end feels the same as before I put my intake on. I think it's merely a placebo effect. Someone says that they lost low end torque and everyones thinks maybe they lost it too. I also think it may have something to do with the increased power in the rest of the rev range. This makes the low end seem weak due to the minimal gains achieved in the low end.

Gabe

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97 Prelude
see it here:Hondaprelude.com

<font face="Verdana, Arial" size="2">Originally posted by Gabe:
Personally, my low end feels the same as before I put my intake on. I think it's merely a placebo effect. Someone says that they lost low end torque and everyones thinks maybe they lost it too. I also think it may have something to do with the increased power in the rest of the rev range. This makes the low end seem weak due to the minimal gains achieved in the low end.
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My sentiments exactly.

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It all has to do with gas velocities, inertia, and scaveging.

Air does not just flow through the intake or exhaust, it flows in pulses. Inertia of the gasses helps scaveging and cylinder filling.

Here's a quick explanation:

At low rpms, you need high gas velocities so that the gas has a bit of inertia to fill the cylinder better on the intake stroke. You also need high exhaust gas velocities so that the inertia of the gas will help "pull" the gas out, like siphoning (also the pulse will help pull the next pulse out, but this has to do with header design).

At high rpms, gas velocities are already high, so port sizes can be larger. Same principles apply, but since the gas is already traveling so fast, the ports need to be big enough so that there is no pressure drop due to a restriction.

The rule of thumb is that a long, small intake/exhaust tube will boost low end power because the gasses will have a higher velocity (thus, higher inertia). Smaller exhaust ports will also promote better scaveging, thus increasing power at lower rpms. Problem is, trying to run small ports at high rpms. The tubing can't support the flow, so you end up choking the engine at high rpms. Now, short, large intake/exhaust tubing promotes better top end power because the tubing can support the higher flow.

So, there is a compromise to be made...make the tubing for low end power or high end, etc. etc.

Header design also plays a role in exhaust performance.

So, now look at Honda's intake design. When the butterflies are closed at low rpms, the intake is a small, long length intake, which promotes low end power. When the butterflies open, the intake tubing is essentially larger, and it appears shorter to the engine, so it promotes top end power.

Whew...that's about all I can think of right now. I know I made some typos, but I am too lazy to correct my spelling!



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Billy
North Texas Prelude Owners Group
www.ntpog.org

<font face="Verdana, Arial" size="2">Originally posted by EBP Lude:
OK, what u guys described makes complete sense! Glad I didn't take up engineering or something back in school.</font>

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Be glad some of us did

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Anyhow, is there anything that I could change to increase tq? No FI is not in my future

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You could try pullies or cam gears. But if you tune the cam gears for low end umph you'll lose some high end.

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BTW- do u hear a lil whining sound when u stand in front of the car at idle? I've been getting this sound since the CAI. Tell me it's the intake pls?

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Yep it's normal.

Gabe

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97 Prelude
see it here:Hondaprelude.com