# cold air intake question



## ahardb0dy (Nov 9, 2003)

instead of replacing the factory airbox and filter with a custom/homemade air intake, what about running pipe from below/behind the front bumper directly into the stock air box either thru the factory opening ( after removing the factory air intake pipe) or thru another area of the factory airbox? Would the colder air being fed in help at all even if it's going thru the stock filter?


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## Crazy-Mart (Jul 14, 2002)

1 sure thing it wont be worst... if you do take it from the factory air box, i might suggest that you shield it from the temperature coming from the exhaust just underneat... using thermo wrap or something like it... when you think of it ... the factory box does have a plastic tubing going near the hood... so imo it might not change anything...


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## SuperHatch (Dec 3, 2002)

If you don't have enough suction, then it won't do anything. It's one thing to have a CAI because it sucks in the cold air, but if you don't have anything sucking cold air, it will just be a pipe, a pipe with a filter, or a combo of the two with insulation wrapped around it... I guess what I'm trying to say is that the pipe has to be able to pull air trough it.. and I don't think that just hooking it up to the stock air box is going to help it pull a lot of air through... You'd have to hook it up to actual TBI... trust me.. I already tried the half-ass rigged version! Haha


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## BII (May 13, 2004)

CAI are a lot of hype anyways, most are made of metal that get heat soaked, which then becomes counterproductive. The one brand that we get the best feedback on where I work is from a company called Volant. Truck stuff though, point is they make thier kits out of some sort of plastic, and many times mimic factory (with the exception of higher flowing filter, larger diameter tubing).


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## ahardb0dy (Nov 9, 2003)

I had one rigged up on my 2001 dakota out of 3" PVC, I heard all kinds of things about how PVC was bad and all but it worked fine and I never had a problem. I was just thinking of what I said in my first post, since no one really makes an adapter that will go directly on the GA16i TB, but I'll make something that will work one of these days.


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## lshadoff (Nov 26, 2002)

bII said:


> CAI are a lot of hype anyways, most are made of metal that get heat soaked, which then becomes counterproductive. The one brand that we get the best feedback on where I work is from a company called Volant. Truck stuff though, point is they make thier kits out of some sort of plastic, and many times mimic factory (with the exception of higher flowing filter, larger diameter tubing).


It's not hype. A true CAI increases horsepower as measured on a dyno. The reason is that when there is uniform diameter tube, it becomes a tuned intake which has a ram effect at a series of rpms which depend on the length of the intake. 

"Perhaps the most potent air intake is the JWT POP combined with the CAI or cold air intake by Place Racing. I have tested this combo and found up to an 8 hp gain with 3 more peak hp. This part is one of my bang for the buck recommendations." [Mike Kojima] 

Lew


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## mille-16i (Jun 16, 2004)

I have to agree with lshadoff alot of the idea behind a Cold air intake is not so much to get cold air but to smooth out the air flow and loose restriction. Think of a engine as a air pump the easier it is to suck in air and to expell it the more power you will free up. You do not Make Power with an intake you free it up cause this is power that would normally go to sucking in air. Don't get me wrong Cold air is a good thing makes for a more effective explosion. 
So if it was me I would get my hands on some ABS (black plastic pipe) that is a little bigger than stock and redo the intake piping with it use the factory air box with a bigger intake hole and some ducting to fresh cooler air and get a K&N filter that replaces your factory one.


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## BII (May 13, 2004)

lshadoff said:


> It's not hype. A true CAI increases horsepower as measured on a dyno. The reason is that when there is uniform diameter tube, it becomes a tuned intake which has a ram effect at a series of rpms which depend on the length of the intake.
> 
> "Perhaps the most potent air intake is the JWT POP combined with the CAI or cold air intake by Place Racing. I have tested this combo and found up to an 8 hp gain with 3 more peak hp. This part is one of my bang for the buck recommendations." [Mike Kojima]
> 
> Lew


A well tuned CAI perhaps. And I should have been clearer. Many CAIs will perform swimmingly on a dyno, and the manufacturer will put out dyno charts and what-not, but what the public is not told is that those big shiny tubes will experience heat soak and not perform as advirtised. Are some better than others? Sure and experience out in the real world will dictate which systems work and which do not, not all are better _per se_. Home brew kits certainly are not very effective for the most part.

Funny thing about new cars, those engineers have designed stock systems that perform pretty well (albiet there is comprimise, the factory will add resonators to reduce noise), and thus the gains will be even less on an aftermarket system.

As much as I "poo-poo" CAI, they are the bread and butter of the company I work for, name the major brand and we sell it (AEM, K&N, Injen, etc).

This is what I mean by the hype. Personally I would not buy a CAI intake made of METAL that will heat up all that nice cold air its pulling from the ground (unless some provision was made to maintain the air cool through the tube).


A homebrew induction tube made of PVC is dangerous, it will get hot and the fumes are toxic.


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## lshadoff (Nov 26, 2002)

Under full acceleration, the air flow through a CAI is laminar. This means that the air is not mixing, and there is a boundary layer along the walls of the tube. This thin boundary layer heats up, but the vast majority of the air never touches the walls of the CAI and is not heated. In order for this to work, the tubing should be smooth, the bends gradual, and nothing present inside the tube to mix the air. The cold air goes through the tube with little heating. 

If you just put a tube into the stock air box, the air is thoroughly mixed, and if the box is hot the air will be hot. Also, there is no resonance effect because the box breaks it up, so the horsepower gains are much less than a true CAI. 

Lew


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## lshadoff (Nov 26, 2002)

I found a post I made to the SE-R mailing list in 1999 where I calculated the resonant frequencies of a CAI and determined the rpms corresponding to those frequencies. Here it is:

The frequency of the fundamental vibrations in an air column is:

f = (n * v) / (2 * l)

v is the velocity of sound (1100 ft/sec.)
l is the length of the tube (in feet)
n is 1/2, 3/2, 5/2,... for a tube closed at one end
n is 1, 2, 3, ... for a tube open at both ends.
(I'm not clear which is the one to use to model the intake of a car.)

Let's calculate the resonant frequencies and corresponding rpms for a pipe of a fixed length 3 feet (The length of a CAI from the filter to the plenum.)

f = (n * 1100) / (2 * 3) = 183.3 * n

Each intake event occurs once every other revolution and there are four events (cylinders) per revolution. Thus there are 2 * rpm / 60 seconds/minute = rpm/30 cycles per second. So.. 

rpm = 30 * f

n : f : rpm
1/2 : 91.65 :	2749
1 : 183.3 : 5499
3/2 : 274.95 : 8248

The "dry" set-up for CAI is about 15 inches long (1.25 feet)

f = (n * 1100) / (2 * 1.25) = 440 * n

n : f : rpm
1/2 : 220 : 6600

What this says is that there are 2-3 rpms where there is resonance with the "wet" set-up and one resonance for the dry.

All the above are a VERY SIMPLIFIED model of the intake. The numbers are therefore only approximations of what really happens.

Lew


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## BII (May 13, 2004)

I thought laminar meant that the air is flowing smoothly, i.e., no turbulence? If that is the case, why would that prevent air from not touching the tube? I'm not necessarily contridicting what you're saying, but I soimply don't understand how this would be. And perhaps the Ram tuning of the CAI compensates for the heat (if any) that lowers the density of the air charge.


The CAI popularity reminds me of how it seems back in the day (and still to this day) all these muscle cars simply have to have "Ram air" or "cowl induction"," which doesn't become effective until the car is at high, sustained speeds. I'm assuming CAIs are simliar, to be effective the car has to be at higher RPM and at WOT, not as effective in everyday type driving.


In any case, none of our e-series motors our going to see a properily tuned CAI anytime soon anyways 

Interesting in any case though.


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## lshadoff (Nov 26, 2002)

Yes, laminar flow means it is flowing smoothly. Therefore the air in the center of the tube stays in the center. It enters cold and never touches a hot surface.

The Place Racing, AEM, and Hotshot CAIs are tuned intakes. All it takes is a constant diameter (large enough not to restrict flow), and a length long enough to produce renonance in the engine's rpm range.

The dyno runs comparing a short ram and CAI indicate that the power gains are in the mid-high rpm range:

"I have extensively tested the CAI and the POP on the dyno and have found that CAI produces more power than the POP alone from 3500 rpm to the fuel cut." [Mike Kojima]

Lew


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## BII (May 13, 2004)

Now I just thought of this, wouldn't closing the throttle cause turbulance and a mixing of the air? Also, like I said, the conditions on the dyno is not going to match "real world" conditions.


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## astreamk1 (Apr 16, 2004)

I had a Volant intake system on my S10. At an idle, it would suck your hand tight against the intake pipe. Even with the throttle closed, I am doubtful there was much standing air in the pipe. 

I think a lot of it has to do with the routing of the piping. The S10's stock air intake piping traveled from one side of the bay to the other via the top of the radiator/fan shroud. Not a very good setup. The Volant intake eliminated all that waste and went off of the throttle body, straight over to the corner of the engine bay away from all that heat. 

Definitely made a big difference.


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## lshadoff (Nov 26, 2002)

bII said:


> Now I just thought of this, wouldn't closing the throttle cause turbulance and a mixing of the air?


Yes, but you measure power at WOT. If the throttle position is not changing, then laminar flow will be established in a CAI 


bII said:


> Also, like I said, the conditions on the dyno is not going to match "real world" conditions.


It is not likely that you will measure a power increase on the dyno that will not be a power increase of some magnitude in the "real world". One problem with dyno measurements is in cooling the engine during a run. Heat soak is more likely than in the "real world". The heat soak produces dyno numbers which are lower than "real world" conditions. If the "real world" conditions are very high ambient air temperature, then the dyno numbers will be slightly higher. 

Lew


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## Popkorn (Nov 16, 2003)

I don't understand the hoopla regarding heat soak. The stock air cleaner on these cars is nothing but a heat SINK. Any CAI setup should be better than stock. But mine runs great with just a K&N filter and the stock setup.


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## BadBoy91 (Jan 21, 2005)

This is so not true. When i first got my 91 SE-R i was pretty broke doin ghetto mods. i used some shop vac tubing, a styrafoam cup, a piece of cardboard, and a bit of 100mph tape ( duct tape) and made a very effective "ram air style" intake system. I simply attached the cup to the lower vent in front fascia, hooked the vaccum tubing to the cup and into the engine bay via resonator box in RF fender well, and cut a peice of cardboard to fit behind the K&N cone filter to retain most of the induced air around the filter and Viola! 100% free CAI. you could get the car good and hot beatin on it pull in the shop take an Infared Thermometer and measure a difference between the area around the filter and the engine bay and see upto an 80 degree difference depending on weather. not only did it feel a bit faster it also made the car run 30-50 degrees cooler on ECT ( i know cuz i hooked up the Consult-II Scan tool) So if your cheap and got half a brain you can make something work, plain and simple.-- sorry i had to edit, i wanted to quote and correct Superhatches post


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## 1989SentraOK (Jan 29, 2004)

And you're saying this worked...hmm...and you hooked it up to the stock airbox? I know that's a different location on a B13, but what if you basically did the same thing with the B12 intake and run the cup down in the lower part of the front bumper so it gets good air, and then run that tubing into where the tube off the stock airbox runs to? Just an idea...it might help a tiny bit, you'll still have to deal with the stock airbox tubing being rectangular/oval but if you look, the tubing stops and it's still in the engine bay, right behind the driver's side headlight and next to the battery. So the air is still a little bit warm. But if you re-route the tubing to somewhere with cooler air, you'd have to think that would help a litle bit, ya know?


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## 1989SentraOK (Jan 29, 2004)

Dude anyone wanna offer some insight? I might try this if it'll work. Only thing I don't get is the styrofoam cup, it seems like that won't breathe well enough to work, and I don't wanna blow inernals or anything.


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## BadBoy91 (Jan 21, 2005)

1989SentraOK said:


> Dude anyone wanna offer some insight? I might try this if it'll work. Only thing I don't get is the styrofoam cup, it seems like that won't breathe well enough to work, and I don't wanna blow inernals or anything.


 I did not use the stock air box actually, it was removed and replaced witha a stillen intake adapter and a K&N cone filter, but i did effectivly make a cold air box, not really ai cold air itake, but same principle. you dont have to the same materials either, thats just what i had on hand at the time. pretty ghetto huh?


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## 1989SentraOK (Jan 29, 2004)

Ghetto fly y0. I still might try that...just gotta get the parts. I'll go look tomorrow and if I find anything i'll let y'all know.


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## BadBoy91 (Jan 21, 2005)

1989SentraOK said:


> Ghetto fly y0. I still might try that...just gotta get the parts. I'll go look tomorrow and if I find anything i'll let y'all know.


yeah man 100% ghetto, just make sure you dont have a problem with it suckin up rain water too. :cheers: good luck though


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## 1989SentraOK (Jan 29, 2004)

Yeah I'm looking for something that will filter it really well, but still cheap. I'm really not looking for performance, just better cooling. I found some shop-vac tubing but it's too small.


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## BII (May 13, 2004)

1989SentraOK said:


> Yeah I'm looking for something that will filter it really well, but still cheap. I'm really not looking for performance, just better cooling. I found some shop-vac tubing but it's too small.


Get a K&N drop-in then.


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## 1989SentraOK (Jan 29, 2004)

Problem isn't filter it's physically how the intake was designed and placed into the car...


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