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Unread 07-04-2008, 11:38 AM   #1
Kiddo86
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My Final Word On Cold Air Intakes

I don't particularly believe that CAIs have a significant effect on performance... but if you're going to do it... the only way to get a TRUE CAI is to build it yourself. There are plenty of write-ups on how to do this, but I thought I'd show off mine too and briefly explain why aftermarket CAI kits are pretty much useless and horribly over priced.

BEFORE


AFTER

... its hard to see in the picture, but the filter is as large as it possibly could be and it sits about 1/3 of the way under the vent... which means I'll have to make up some sort of shield for rainy days eventually.


You can see in the before photo that I tried to make up a "ram air" previously. The problem with this design is that the stock air intake provides plenty of flow already (making a "ram air" design useless) and I actually relocated the filter to the worst possible location too. The next time you park your jeep after a long drive, feel the body all around the engine bay... You will find (as you might guess) that the hood is the hottest. This makes perfect sense since heat rises and it also means that I had put my air filter right where the air is the warmest.

Relocating the filter to behind the firewall was about a 1 hour project and it cost me $12. I only had to buy a 2.5" sleeve, a PVC joint, and a longer tube for the breather.

Assuming that getting denser air into a combustion chamber is effective, the equation that supports the use of a CAI is simple...

(DENSITY) = (PRESSURE) / (CONSTANT)X(TEMPERATURE)

... since air pressure and the constant remain the same, there is a 1:1 correlation between the temperature of the air that enters your engine and the density of that air. I don't know enough about engines to say how much it matters (please chime in if you do) but relocating the air filter to bring colder air into the engine definitely DOES get more air molecules into the combustion chambers by means of air density.

The end result...

1) If ANY cold air intake is capable of helping performance on a wrangler, mine would be one of them since I'm now pulling air 100% from outside of the jeep.
2) It sounds frickin' awesome! Having the filter located the way it is almost makes driving more fun as I get to listen to some pretty wild sucking sounds or rumbling depending on what the RPMs are.
3) When I have more time to kill, I'll find a more permanent design than duct tape for sealing the hole in the firewall... I think some black insulating tape thats been neatly trimmed to fit should work nicely. I'd also like to paint the PVC joint with some Black Krylon Fusion.

oh... and here is my jeep!



Last edited by Kiddo86; 07-09-2008 at 03:33 PM..
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Unread 07-04-2008, 11:41 AM   #2
1BadTJ
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nice work, good looking jeep. i live by the premise that the factory intake is more than sufficient for the 4 liter.
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Unread 07-04-2008, 11:43 AM   #3
TheBoogieman
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Quote:
Originally Posted by Kiddo86 View Post
Fist off... could someone repost this click-free since I still can't figure that one out?

I don't particularly believe that CAIs have a significant effect on performance... but if you're going to do it... the only way to get a TRUE CAI is to build it yourself. There are plenty of write-ups on how to do this, but I thought I'd show off mine too and briefly explain why aftermarket CAI kits are pretty much useless and horribly over priced.

BEFORE


AFTER

... its hard to see in the picture, but the filter is as large as it possibly could be and it sits about 1/3 of the way under the vent... which means I'll have to make up some sort of shield for rainy days eventually.


You can see in the before photo that I tried to make up a "ram air" previously. The problem with this design is that the stock air intake provides plenty of flow already (making a "ram air" design useless) and I actually relocated the filter to the worst possible location too. The next time you park your jeep after a long drive, feel the body all around the engine bay... You will find (as you might guess) that the hood is the hottest. This makes perfect sense since heat rises and it also means that I had put my air filter right where the air is the warmest.

Relocating the filter to behind the firewall was about a 1 hour project and it cost me $12. I only had to buy a 2.5" sleeve, a PVC joint, and a longer tube for the breather.

Assuming that getting denser air into a combustion chamber is effective, the equation that supports the use of a CAI is simple...

(DENSITY) = (PRESSURE) / (CONSTANT)X(TEMPERATURE)

... since air pressure and the constant remain the same, there is a 1:1 correlation between the temperature of the air that enters your engine and the density of that air. I don't know enough about engines to say how much it matters (please chime in if you do) but relocating the air filter to bring colder air into the engine definitely DOES get more air molecules into the combustion chambers by means of air density.

The end result...

1) If ANY cold air intake is capable of helping performance on a wrangler, mine would be one of them since I'm now pulling air 100% from outside of the jeep.
2) It sounds frickin' awesome! Having the filter located the way it is almost makes driving more fun as I get to listen to some pretty wild sucking sounds or rumbling depending on what the RPMs are.
3) When I have more time to kill, I'll find a more permanent design than duct tape for sealing the hole in the firewall... I think some black insulating tape thats been neatly trimmed to fit should work nicely. I'd also like to paint the PVC joint with some Black Krylon Fusion.

oh... and here is my jeep!
I love your Jeep.
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Unread 07-04-2008, 11:44 AM   #4
Kiddo86
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1BadTJ...

You're absolutely correct. I would say that this, like almost all of my other jeep projects, was done mostly because I just love to have something to work on.
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Unread 07-04-2008, 12:09 PM   #5
RVA_TJ06
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do you get a lot of water on that filter being that it is open to the elements??


nevermind I see you will eventually address that issue.
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Unread 07-04-2008, 12:13 PM   #6
Kiddo86
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Originally Posted by RVA_TJ06 View Post
do you get a lot of water on that filter being that it is open to the elements??


nevermind I see you will eventually address that issue.
Yea... I normally take it out either to wheel it or for a pleasure cruise... my daily driver/rainy day vehicle is an 96 grand cherokee. But I will be building a shield soon... I don't want a jeep that can't handle a bit of rain!
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Unread 07-04-2008, 09:20 PM   #7
George Dickel
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Very nice. How about a parts list?
I'll be tackling that one soon. I need more air for the stroker but REFUSE to pay $250 for CAI. I bought an off-brand one for my Stang for $80 that actually takes in air from the fenderwell. It works great and probably better than the $300 jobs!
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Unread 07-04-2008, 09:37 PM   #8
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Good job.. I agree with your summation. It has to be cooler that sucking it from under the hood. I am Banksed up and feel like I am sucking that hot under the hood air.. I am! No feeling about it. It is even warmer than the ambient in the cooler months I imagine but I get such great throttle response as compaired to factory set up. It's major quick but man that hot air. anyway, you JP looks great.
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Unread 07-04-2008, 11:06 PM   #9
Kiddo86
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Quote:
Originally Posted by George Dickel View Post
Very nice. How about a parts list?
I'll be tackling that one soon. I need more air for the stroker but REFUSE to pay $250 for CAI. I bought an off-brand one for my Stang for $80 that actually takes in air from the fenderwell. It works great and probably better than the $300 jobs!
As far as a parts list goes... "cheap" is all you need to know. I bought parts according to a set up I saw on here and ended up taking it all back because my firewall turned out to be a bit different than the one I read about and my filter was too big to fit the way I had seen.

For my 98' 4.0 TJ, all I needed to buy was...

-filter
-rubber joint
-45 degree PVC knuckle
-longer hose for the breather

You can get it done for under $20 for sure if you already have a filter. If you go with a smaller filter, you can put the filter in at an angle and all you need is a few inches of 3" pipe and a clamp.

The only hard part about the entire project was drilling the hole in the firewall. Mine ended up a bit bigger than I wanted because I drilled before I realized that the filter was sitting in the way of my windshield wiper components (when active) the way I originally planned it.
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Unread 07-05-2008, 10:08 AM   #10
Railroadgin
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Does the computer compensate for the extra air intake?
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Unread 07-05-2008, 10:46 AM   #11
Kiddo86
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Quote:
Originally Posted by Railroadgin View Post
Does the computer compensate for the extra air intake?
This seems to be the central question!

I BELIEVE that the computer senses air intake by volume, and not by density. I suspect that the computer is simply making sure that the same volume of air is available for each ignition and having a TRUE cold air intake causes the same amount of air volume to contain more molecules (and therefore more oxygen) in each fire.

There's no question about weather or not colder air gives more oxygen per unit volume... that part is basic chemistry. The only real unknown is how effective the additional oxygen is in providing a greater, more complete burn. In my opinion... the range of effect depends entirely on the specific engine that the CAI is being applied to.

But to answer your question... Yes and No. Yes, the computer compensates for volume and no, it doesn't compensate for density. This is why RAM AIR intakes do NOTHING on the 4.0. The idea of a RAM AIR intake is to eliminate all resistance with a shorter, wider tube and a high flow air filter.... the the 4.0 has no problem pulling the air it wants through a complete stock air intake. Replacing your entire intake system with just a K&N filter sitting on top of your throttle body wont change the volume of air you pull in... in fact, you would be getting warmer air than the stock intake so it would probably be a bad thing.

It's REALLY important to note that every intake system you see on Quadratec or anywhere else is advertised as "cold air intakes" but they are actually just "ram air intakes" since the air is coming from the same (or close to the same) spot... so don't waste you're money.

Last edited by Kiddo86; 07-05-2008 at 10:56 AM..
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Unread 07-05-2008, 01:48 PM   #12
littledevilTJ
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i would do that but im afraid rain water would get sucked up into it.
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Unread 07-05-2008, 01:55 PM   #13
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Looks good. Move the IAT sensor onto the intake tube. I had to extend the wiring and buy a new sensor so that the old one keeps the hole plugged up on the air intake. When Jeep put the sensor in the manifold, it heat soaks the IAT and causes the computer to think the air coming in is really hot. I drilled a 3/4" hole in the intake tube and put in a rubber gromet and put the new IAT into that hole. This is why Jeep moved the IAT on 05 and 06 Jeeps.
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Unread 07-05-2008, 02:19 PM   #14
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Kiddo, that CAI setup is innovative and wicked cool

Can you put a hood scoop on it? jc whitley has hoop scoops that can be modified and fit with the vent removed.

Any other performance product on it? Like headers and a freeflow exhaust system?

If your jeep had a soul ,it would be a supermodel
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Unread 07-05-2008, 06:05 PM   #15
Kiddo86
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Quote:
Originally Posted by supajeep View Post
Kiddo, that CAI setup is innovative and wicked cool

Can you put a hood scoop on it? jc whitley has hoop scoops that can be modified and fit with the vent removed.

Any other performance product on it? Like headers and a freeflow exhaust system?

If your jeep had a soul ,it would be a supermodel
Thanks! Yea, I have some other mods... but only because the original stuff broke. I replaced the entire exhaust system with banks/magnaflow stuff and my ignition is all MSD. I've thought about a hood scoop... but I don't think it would do much.
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