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Kansas Chainsaw Massacre
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I decided to make this thread because of the sheer amount of mis information that's circulating on how the stock Si intake actually works. I think most of this information can be blamed on American Honda- they advertise that the stock Si intake works "like a cold air intake," and most people think this means it must take air from the bottom of the engine bay somewhere, which is incorrect.

Here's a diagram to get us started:


this is a diagram of a standard intake tract and a mugen intake tract for a JDM civic (FD2). Our intake tract is set up exactly the same way. in the "STD" diagram, you can see that the air is coming in through the top of the fender, going down into the resonator (which contains a series of pipes to quiet and "tune" the sound of the air), and then back up to the airbox and finally through the throttle body.

here's a picture of where the Si's snorkel ends- jammed up right in the fender behind your battery tray.

if you have a stock intake system, go out and look in your engine bay. you'll clearly see the intake.

So, why did Honda advertise their intake as a "cold air system?" quite technically, it is. Most people think "Cold air" means the air must come from the bottom of the car somewhere, but really the air just has to be cold (and therefore isolated from the engine bay). Many cars have an intake system that simply pulls air from somewhere in the bay, and because Honda's Si intake is isolated, they can market it this way and technically be correct.

There are many reasons that the stock intake system is set up the way it is, but first and foremost Honda had to think about practicality. they are selling a car that must be able to drive in many conditions safely and without failure. therefore, it is practical to have the intake pull air from a high location. Thankfully Honda actually DID think about power and sound when they designed this intake system. For a stock system, it's not half bad at all!
 

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So the only reason why an aftermarket CAI gains over the stock "CAI" is because of less piping? Or does the placement of the aftermarket CAI actually draw colder air than the stock "CAI?" And if it does draw colder air than stock, could we just do some sort of hack-n-slash-air-dam on our fender to make the stock "CAI" more powerful? :popcorn:
 

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The aftermarket intake is less restrictive.

Also doesn't the engine pull in the air? Not the intake.
Ditto. It's less restrictive because there's less piping and no intake resonator box.

Yes, the engine pulls the air by vacumn action, caused by the internal combustion cycle in our naturally aspirated engines. If you managed to come up with some sort of 'ram-air' that scoops air that runs over the top of the hood, etc., then that would be something like forced induction of air.
Of course, true forced induction is what you have when you have a turbocharger.
 

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Kansas Chainsaw Massacre
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Discussion Starter #6
So the only reason why an aftermarket CAI gains over the stock "CAI" is because of less piping? Or does the placement of the aftermarket CAI actually draw colder air than the stock "CAI?" And if it does draw colder air than stock, could we just do some sort of hack-n-slash-air-dam on our fender to make the stock "CAI" more powerful? :popcorn:
1) less restrictive piping (as was mentioned)
2) less restrictive filter
3)greater filter surface area (if you were to cut a conical filter from an aftermarket intake and lay it flat, it would have a greater surface area than the stock panel filter)

I would definitely say a CAI is taking in air that is somewhat colder than the stock system, and yes, you can hack-n-slash-the-air-dam-to-your-content. A lot of people have.
 

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in my opinion, the stock intake provides minimum cold air with good flow. if you have a short ram, its the same as stock intake because its less restrictive, but pulls in more hot air, so it evens out. if you have a cold air intake, its brings cold air and its less restrictive which equals more power.
 

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Kansas Chainsaw Massacre
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Discussion Starter #8
in my opinion, the stock intake provides minimum cold air with good flow. if you have a short ram, its the same as stock intake because its less restrictive, but pulls in more hot air, so it evens out. if you have a cold air intake, its brings cold air and its less restrictive which equals more power.

if the stock intake is on the level with a SRI, why do SRI's have measurable, feelable power gains over the stock intake system? *raises an eyebrow* the stock intake system is a very well designed system made to keep your car quiet, and to keep your car from sucking up water. that is all.
 

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1) less restrictive piping (as was mentioned)
2) less restrictive filter
3)greater filter surface area (if you were to cut a conical filter from an aftermarket intake and lay it flat, it would have a greater surface area than the stock panel filter)

I would definitely say a CAI is taking in air that is somewhat colder than the stock system, and yes, you can hack-n-slash-the-air-dam-to-your-content. A lot of people have.
Indeed, thank you for answering my questions, and good idea for a sticky. Kudos! :clapping:
 

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in my opinion, the stock intake provides minimum cold air with good flow. if you have a short ram, its the same as stock intake because its less restrictive, but pulls in more hot air, so it evens out. if you have a cold air intake, its brings cold air and its less restrictive which equals more power.
An SRI would be much less restrictive than the stock intake.
A CAI would be less restrictive than stock, too, though not as free-flowing as an SRI.
The trade-off:
SRIs have less restriction, but higher intake air temps
CAIs have a little more restriction than SRIs, but have lower air intake temps.
 

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Kansas Chainsaw Massacre
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Discussion Starter #13
from my experience, i felt no gain with SRI. the only gains was the extra loud sound.
"feeling" a gain is not the same thing as measuring it. on this premise, a car with lots of low-end torque (like a stock GTI) should be tons faster because you can "feel" the power?
 

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What about for a Civic Lx? I cant remember for sure but there was the box at the bottom behind the mudflap that we removed, if it draws air from around there then would getting a CAI really make much of a difference?
 

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Very interesting thread. I have the Injen SRI that's supposedly the first "tuned" intake on the market. Is that true because I thought we couldn't tune our cars yet other than a reflash?. I did however feel a nice gain in the "vtec pull" when I installed the SRI. The only reason why I didn't go with the CAI was because my buddy soaked up water in his 350Z and totally demolished his engine; had to trade-in for another car.
 

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Very interesting thread. I have the Injen SRI that's supposedly the first "tuned" intake on the market. Is that true because I thought we couldn't tune our cars yet other than a reflash?. I did however feel a nice gain in the "vtec pull" when I installed the SRI. The only reason why I didn't go with the CAI was because my buddy soaked up water in his 350Z and totally demolished his engine; had to trade-in for another car.
yeah tuned to that test car they ran the dyno on, the intakes might be built the same but i think you still need to get in to the computer and tune it for that intake but the only thing ecu wise we can do is a reflash i might be wrong. i'm waiting for either the mugen intake (that is hard to find) or a spoon drop in (that i can't find either) for right now i'm good with stock play it safe thats just me though. sounds like your buddy needed a by pass i know aem makes one for there cia
 

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Very nice info here, Thanks ErichPryde :thumb:

I was so undecided with all the info on SRI's and CAI's that Im playing it safe for now and just ordered a K&N drop in filter for $38 with my commercial account at Advanced and i guess ill see how that works out for me.
 
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