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FAQ - Cold Air Intake

254K views 340 replies 105 participants last post by  Knuckelhead 
#1 · (Edited)
Disclaimer: This is info I gathered and some of it may be my personal opinion...in no way intended to be all-knowing fact or infallible. Do your homework, read what's presented, and make your own informed decision.

The question is frequently asked: "Do cold air intakes make a difference?", whether this be improving gas mileage or improving performance.

the simple answer is NO. If you're interested why, read further.

A Problem:
ISO Coarse Dust Test of multiple brands of air filters - K&N clog faster and passes 3-4x more dust than paper filter:ISO 5011 Air Filter Test Report

They state: "Compared to the AC Delco air filter, the "K&N" plugged up nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt."

Fine dust passing through a "K&N" in the stock TJ airbox:
How good are K&N filters?

Why does this matter? Dust = silica. Read about silica here:
Recognizing the Signs and Symptoms of Silica Contamination from Practicing Oil Analysis Magazine, January 2006.

The UOA (used oil analysis) with observed silica content in street driven vehicles:
Threw away K&N's due to high silicon in UOA's - Bob Is The Oil Guy

Cold Air Intake Design:
There are three main types:
1. Stock intake tube cut with a "K&N" cone style filter from local autoparts store clamped on the end.
2. An aftermarket tube, usually larger in diameter than stock, with a "K&N" cone style filter clamped onto it. Many utilize a 'heat' shield, and some utilize a "dry" filter instead of the "oiled" types.
3. Other intake options use a snorkel of some type, to draw air from outside the engine compartment (covered later).

Performance Gains:
Here is a dyno test performed by JP Magazine:
Jeep Wrangler TJ Inktake Dyno - A Day On the Dyno - Jp Magazine

Notice they showed a gain of 6 hp and 4 lb-ft of torque at around 4500rpm.

Here's a link to a 18 comprehensive dyno runs comparing the stock intake, no intake at all and an aftermarket cowl intake.
http://www.tricktuners.com/forums/showthread.php?t=226
He saw absolutely no statistically significant difference between the runs. And to actually show how easy it is to skew a dyno, he saw a near 10 hp increase just by changing tire pressure.

Have you ever wondered what the Jeep Engineer's would have to say about the stock intake vs a CAI?
well, read about that here: JeepEngineers on Cold Air Intakes.

So What Do We Know about Cold Air Intakes:
Pros:
1. Eliminates stock airbox (may be necessary for custom fenders)
2. Improved HP and TQ by about 2-3% at ~4500rpm (Engine max: 5200rpm).

Cons:
1. Expensive - brand name kits cost around $150+
2. Cleaning - open element filter is exposed to much more dirt, mud, dust and debris from engine compartment.
3. Thin film of dust typically passing through filter, thus the engine is exposed to this dust.
4. Oiled filter versions further attract dust, dirt and debris.
5. Due to inadequete filtering, a Outwears Pre-filter, or similar filter sock is required, further adding to cost.
6. Requires frequent cleaning due to dirty environment - typical cleaning kit costs $20+.
7. Increases risk of hydrolocking - exposed element can suck water into engine easily.
8. Noise - annoying "sucking" noise can be heard, sometimes associated with a loud whistle.
9. Dirty filter can cause rough and/or high idle.

I used to run an AEM intake, but removed it after finding a lot of problems associated with it. I documented my observations here: AEM Intake observations

The Snorkel:
There are also many brands of snorkels, designed to prevent water from getting into the engine, and to introduce air from outside the engine compartment. Brands include ARB, Volant, and others. Many people construct their own snorkel systems using PVC pipe and 1990's Buick intake boxes.

Pros:
1. Introduces air from outside the engine compartment
2. Elevated air intake to resist hydrolocking engine during deep water crossings.

Cons:
1. Expensive - ARB, Volant, etc brand intakes cost over $300.
2. Most require extensive modifications to the stock airbox, or a new airbox.
3. Modifications often require drilling and cutting of the body - could lead to rust, or water leaks.
4. Often times the windshield cannot be folded down.

Alternative DIY & Snorkel Write ups:
Buick/Hummer snorkel #1: TJ Hummer Intake Write-up (Buick Airbox)
Buick/Hummer snorkel #2: Write-up for a Hummer cold air intake
Low buck Buick airbox: Buick Airbox instalation
Homemade Cowl CAI #1: My Final Word On Cold Air Intakes
Homemade Cowl CAI #2: Cowl Induction - snorkle (WRITE UP)
Another cowl intake: Cowl Induction - snorkle (WRITE UP) - Page 4
Autozone Cowl intake: http://www.jeepforum.com/forum/f9/cold-air-intake-860538/
Buick airbox mounted directly to the throttle body: http://www.jeepforum.com/forum/f9/i-am-liberated-863818/
Homemade snorkel with K&N: http://www.jeepforum.com/forum/f9/homemade-snorkel-intake-w-pics-910113/

My personal favorites:
Windstar Airbox Cowl Intake: http://www.jeepforum.com/forum/f9/cowl-intake-windstar-air-box-566973/
Windstar Airbox Cowl Intake #2: http://www.jeepforum.com/forum/f9/windstar-cowl-intake-1064377/
Mustang Air box CAI: Mustang GT Air Cannister
Homemade Aluminum Snorkel: homebrew aluminum snorkel

Fun video:

 
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#2 · (Edited)
Cost Effectiveness:

$250 for a cold air intake system
- let's say this will get you 20,000 miles before requiring cleaning
$20 for cleaning kit
- this will get you about another 20,000 miles

In contrast, for the stock airbox:
paper filter cost from local auto parts store: ~$14

This means for the ~$250 the CAI cost, you could have bought 18 paper filters. Considering you can get about 6,000-9,000 miles from each paper filter, that means you could travel at least 108,000 miles on $250 of paper filters.

For the cost of one CAI, and one cleaning kit, used to travel approx. 40,000 miles, you could travel ~120,000 miles on paper air filters.

It is simply not cost effective for 3% in power gains @ 4500rpm to jeopardize your engines health, or to waste money on expensive filters mechanisms.

Volumetric Efficiency:

The argument is often made that more air = more fuel and therefore more power. Well, first you should probably know the air requirement of the engine, so you can actually determine if the air intake is somehow restrictive. Engine Air Flow requirements are measured in CFM (cubic feet per minute)

Calculating the CFM of air required for an engine is pretty simple.

CFM = (CID x RPM x VE)/3456

For our 4.0L (4.0L = 244 cubic inches displacement):

If we assume 100% efficiency: (244 cu-in) * (5200 RPM-redline) / 3456 = 367 CFM
...but unforunately our engines are nowhere near 100% efficient, 80-90% is more reasonable for a modern engine.

So, in reality we have: (244 cu-in) * (5200 RPM) * (.85) / 3456 = 312 CFM

Well, Four Wheeler magazine tested a stock throttle body and found it flowed 450 CFM! Obviously that's even more than an ideal, non-real-world 100% efficient 4.0L!

They also did some extensive flow testing with a 4.7L stroker, and found it only used 383 CFM!
Source: http://www.fourwheeler.com/techarticles/engine/129_0712_2000_jeep_wrangler_40l_inline_6/viewall.html

Now, let's work backwards and figure out how efficient their high performance 4.7L stroker was:

We have: (289 cu-in) * (5200 RPM) * (.88) / 3456 = 383 CFM

So with more displacement, higher compression ratio, a modified head, valve job, performance cam and some other work, they were able to acheive 88% efficiency in this context...yielding 225 hp @ 5k RPM & 280 ft-lbs @ 4k RPM, at the crank.

Now let's look at the numbers....their performance stroker yielded 35 hp/45 ft-lb gain over stock (~16% increase)....for a few grand.

Think about that next time you read an advertisement that suggests a given percentage increase in hp/tq.

Here's more tech & math if you're interested:
http://www.epi-eng.com/piston_engine_technology/volumetric_efficiency.htm
 
#3 ·
Nice :thumbsup:

Now we just need one for:
Throttle Body Spacers
Hi Lift mounts
How to increase MPG and power
etc
etc
etc.
 
#5 · (Edited)
I documented my observations on the AEM Throttle body spacer and a 62mm bored TB here:
http://www.jeepforum.com/forum/showpost.php?p=5116179&postcount=16

robplumm said:
K&N cleaning kit is 9.99. You get multiple uses out of it
My google search has shown each kit costing 19.95 from three different websites. My AEM intake was so dirty after 25,000 miles, I used the entire cleaning kit provided by AEM. I purchased a K&N Recharge kit, which is now 1/2 empty to clean the filter again at 30,000 miles. Every time the filter was cleaned it was caked with dirt, dust, mud and debris, resulting in high engine idle (900-1200rpm) and rough idle (sputtering).
 
#6 ·
This is excellent info. I have always known the filters offer little bang for the buck. Especially where I live at high altitude.

What I would really like to know, is some definative answer as to the benefits to a true cold air intake. Moving the filter to the cowl is relatively easy, or you can use a snorkel. In theory there is supposed to be an advantage, but I want to know what is real life numbers.

I want to do a cowl induction and also install vents in my hood, I wonder what the real benifits would be.
 
#7 ·
Good info. But. It is not a "cold" air intake unless it gets the air from someplace other than under that hot hood IMHO. I think AEM calls theirs a "Cool" air system, it may be someone else. You will not see any significant power gains unless you are actually getting cold air. This means air from elsewhere than under the hood and an insulated intake pipe. Most, if not all intakes they sell on the after market pick up air from the same place the stock system does. All that hot radiator air is coming right into the intake. Some of the systems put a dam affair in there, but I seriously doubt it is very effective. I am not knocking any intakes out there, but I would not call them a CAI unless they were getting the cold outside the hood air. My intake is sealed off from the hood and pulls air in from the cowl. The intake tube is also insulated. My "seat of the pants" dyno was very impressed. I would love to see dyno readings on this system. I have not checked mileage yet, but others are averaging betwen 50 and 70 more miles per tank. If they can get the price right on this deal it'll sell like hotcakes. It also filters the A/C air so the cab and vents stay cleaner.
 
#8 ·
Pics, pics, pics....

I would also agree the intake tube needs to be insulated. Plastic is not as conductive as those nice shinny thin aluminum ones. Not only that, but the intake it's self is very condustive and stays quite hot. On my XJ I insulated my header and the bottom side of my intake trying to keep the exhaust heat away. Honestly, I don't think it helped any. The underhood temps were still hot and the aluminum intake bolted to the block seemed to be just as hot as before.

So again, the cowl intake and hood vents sound good in theory, just not sure what it will amount to when I'm done.
 
#9 ·
OK sooooo
Bear with me on this cause Im a newbie trying to figure things out...

From what I am reading... there is no need to put anything other than the K&N air filter I have on there ( which did put the purr back in my engine) ...
 
#12 ·
ARGH! What is the reasoning behind that?? They seem to work great?:confused:
People just have their own opinions and some facts:DHere's the best quote on them.
"The added dust and fine particulates a K&N has been found to pass when compared to a paper element filter like from AC-Delco makes the K&N a very poor choice in my opinion. Beyond that, it won't give better mpg or performance despite what their wild marketing claims say. This has been well proven in studies that have been shown and discussed here before. One study shows the K&N passed 18X more dirt & clogged up 3X faster than an AC-Delco paper air filter if I recall correctly."
 
#20 ·
...Notice they showed a gain of 6 hp and 4 lb-ft of torque at around 4500rpm....
I dynoed my Mustang and I saw a 5.3 HP gain & 6.1 lb-ft torque gain from the 1st pull compared to the 3rd pull and each time the engine was fully up to operating temperature. I might believe the JP magazine gains if the magazine ran 10 pulls without the intake add-on installed and then 10 pulls with the intake add-on installed. Then the differences noted between each pull before and after was a minimum 6hp, I would honestly say that the pipe give a 6hp gain. Otherwise it's snake oil.
 
#24 ·
just sold my AEM Cold Air Intake + throttle body spacer for 50 bucks. oil style filter and all. I can tell you the TB spacer doesn't do squat, I ran it for the past 6 months or so with a 63mm TB, and there is no difference with or without it. The 63mm TB however does breath better at higher RPMs, and you can feel it when you downshift on the highway.
 
#25 ·
Volant Cold Air Intake Review

I did a lot of research figuring out what to get and thought I would write a quick review in case someones interested.

In JP magazines April 08 issue. They test 10 different CAI units and dyno test the results compared to stock. Almost every CAI actually added 10 hp and 10ft pounds of torque over stock.

When I started shopping for CAI's I thought it would be a good idea to leave the option open to add a snorkle down the line. Volant is the only one that makes an enclosed air box on their CAI so you can attach a snorkle later.

If you don't like the look of the Volant snorkle it would be pretty easy to hook up ARB's instead.

The kit installed in about 15 minutes and used the old airboxes bolt holes through the fender. The air box, filter element and ducting are all way bigger than stock.

Is there more power? Not until you go over 2,000 rpm and are really heavy on the skinny pedal. Also when you floor it there is more engine noise, but in a good way. Like a custom exhaust has been installed.

I like driving fast and appreciate feeling a little more power during acceleration. I also tested it going up hills that I am used to driving and the jeep didn't need to downshift as much.

Below 2,000 rpm and under normal driving conditions there really isn't any difference.

Mine cost just under $300 so its on par or cheaper than the other brands. All in all it works and I would recommend it!

Happy jeepin!
 
#32 ·
I did a lot of research figuring out what to get and thought I would write a quick review in case someones interested.

In JP magazines April 08 issue. They test 10 different CAI units and dyno test the results compared to stock. Almost every CAI actually added 10 hp and 10ft pounds of torque over stock.

When I started shopping for CAI's I thought it would be a good idea to leave the option open to add a snorkle down the line. Volant is the only one that makes an enclosed air box on their CAI so you can attach a snorkle later.

If you don't like the look of the Volant snorkle it would be pretty easy to hook up ARB's instead.

The kit installed in about 15 minutes and used the old airboxes bolt holes through the fender. The air box, filter element and ducting are all way bigger than stock.

Is there more power? Not until you go over 2,000 rpm and are really heavy on the skinny pedal. Also when you floor it there is more engine noise, but in a good way. Like a custom exhaust has been installed.

I like driving fast and appreciate feeling a little more power during acceleration. I also tested it going up hills that I am used to driving and the jeep didn't need to downshift as much.

Below 2,000 rpm and under normal driving conditions there really isn't any difference.

Mine cost just under $300 so its on par or cheaper than the other brands. All in all it works and I would recommend it!

Happy jeepin!
I have the Volant CAI & Snorkel installed in separate occasions. If you liked the Volant CAI, you will love it with the snorkel.
I have the same feedback as yours, but with the snorkel, it's even better.

Update:

I've been monitoring the IAT via my ScanGuage vs the ambient temp via the auto dimming mirror. I've got the horn removed on the stock airbox. So far the past 2 weeks, the highest temp I've seen out of the IAT has been around 80*F - with an ambient temp of about 50*F, and that was when idling at a long stop light. The faster the vehicle travels, the colder the IAT gets - even down to 30*F on the highway when its ~15*F outside. So far on the street the actual intake temp seems to run at twice the ambient at the hottest while idling. As soon as you start moving it drops.
I installed my Scan Gauge after installing my Volant CAI. The Volant CAI still sucks hot air from under the hood as a divider to block engine heat from the intake is not included in the kit (but can be easily made) and the intake in still under the hood.

The outside air temp in where I live is constantly 90-deg during the day. With the Volant CAI, start-up temp, as shown on Scan Gauge's IAT reading, shows on average 135-deg. and warmed-up engine is usually around 180-deg. With the snorkel, start-up temp is at 90-deg. with warmed-up temp average at 120-deg.

Just posting this as a contribution for everyone's reference based on my experience.
 
#26 ·
Update:

I've been monitoring the IAT via my ScanGuage vs the ambient temp via the auto dimming mirror. I've got the horn removed on the stock airbox. So far the past 2 weeks, the highest temp I've seen out of the IAT has been around 80*F - with an ambient temp of about 50*F, and that was when idling at a long stop light. The faster the vehicle travels, the colder the IAT gets - even down to 30*F on the highway when its ~15*F outside. So far on the street the actual intake temp seems to run at twice the ambient at the hottest while idling. As soon as you start moving it drops.
 
#27 ·
So it's sucking cold air. Interesting. I'd like to see results of this in the summer as well. Another reason for me to get a scan gauge I guess!
 
#31 ·
Bigbob:
Glad to see someone else is speaking out FOR CAI's!! ive felt very alone about posting for them when everyone else hates them. im starting to think the main difference in how people feel they work may have to do with the IAT sensor being in the tube instead of the manifold. (mines in the tube)!!!
 
#34 ·
Yeah, I need to get a scan gauge. I am pretty sure my air temps are lower at the tube mounted IAT sensor. I do have a good air source and my intake tube is insulated.

A under the hood air cleaner calling itself a CAI is not gonna improve things. It still gets the same warm air from the same source the stock set-up does! That dirt and junk getting flung off the fan is carried to the filter by hot radiator air. There has been no one I can think of who has the CAI I have who is not impressed with the power difference or I guess it's driveability more than actual power. And when you say CAI vs Stock I am presuming you are comparing stock to the AEM CAI which is available? I am pretty sure the AEM CAI is not a CAI just called that as a sales pitch. If you are getting the air source from under the hood it is not a cold air intake.
 
#36 ·
I'm not going to say anything in this thread other than these few things.... Personally, I don't believe a "cold air intake" does enough for a Jeep engine the way Jeeps are driven to benefit enough to notice. Butt-dynos aren't exactly accurate. Then, you'll never see an automotive magazine do a review of products made by their advertisers where they won't find nice things to say about them... they are advertisers afterall. And the way dynos work, the gains they write about are down in the noise level and I personally believe are "tweaked" to show something was gained.

Our Jeeps aren't racers and packing more air in because it's denser because it's colder isn't going to make any difference unless you're driving at extremely high rpms and at wide-open-throttle regularly.... not how many of us non-younger aged guys drive our Jeeps.

Personally, I wouldn't install a cold air intake if one were offered to me for $1.98. And if it had a K&N air filter on it, I wouldn't install it even if you paid me. :)
 
#40 ·
Just for fun let's look at some of the new testing from Amsoil. The test result posted by Jerry is not accurate as far as the Amsoil filter result. The TS filter in that test was an oiled foam style filter. In 2006 Amsoil introduced it's Nano-Fiber Synthetic media filters. The EAA filters are a dry media that can be cleaned with low pressure air or a shop vac, no oiling. It is guaranteed for 4 years or 100,000 miles The nano fibers can actually catch smaller particles than the Cellulose (paper) media. It also holds more of those particles without clogging. Amsoil partnered with Injen technologies to use those filters in a line of cold air kits. There are over 150 applications, gas & diesel, including the TJ's & KJ's.
http://www.amsoil.com/redirect.cgi?zo=1468345&page=storefront/injen

Not trying to "stir it" with this post, just presenting more information for everyone to look at. Hopefully this will help someone.
 

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#59 ·
Not trying to "stir it" with this post, just presenting more information for everyone to look at. Hopefully this will help someone.
I will NEVER use a test by the maker of the item being tested for the true information...never. Useless, shouldn't even bother...

Also on a side note:
I use a True Flow filter with a K&N FIPK cai, just so it is known what/where with me.

True flow says NOT to use a pre filter. Don't know why, but I called them and was told "no pre filter".
 
#44 ·
Cai

Ok guys, I am looking to get a jeep soon. My current car is a 2003 hyundai tiburon GT with some mods done to it, but I have no room in the thing. It is one of the smallest 2 door coupes you could ever fit in. That and the fact that the trunk is filled up with 2 12" inch sony xplod subs.

But enough with the rambling, cold air intakes are very useful. For one, they do add a slight horsepower gain, obviously you will notice the gain more on a sports car than a jeep. And you don't have to worry about hydrolock unless your driving through a river. My car is barely off the ground(1-2 feet) and I drive with my cai in ANY type of condition. Now the cai pulls out cold air to the engine from the bottom. The air gets sucked in pretty close to where your left front tire would be. This makes it away from the engine compartment so it doesn't suck in hot air instead.

And yes, I think the whistling sound it makes and the swooosshh! sound it makes when sucking in sounds great. It's like a cargasm! lol.

I know this is a jeep forum, but here is a little vid of what my cold air intake sounds on my car:
Note: please disregard the exhaust sound in the background.
 
#46 ·
Ok guys, I am looking to get a jeep soon. My current car is a 2003 hyundai tiburon GT with some mods done to it, but I have no room in the thing. It is one of the smallest 2 door coupes you could ever fit in. That and the fact that the trunk is filled up with 2 12" inch sony xplod subs.

But enough with the rambling, cold air intakes are very useful. For one, they do add a slight horsepower gain, obviously you will notice the gain more on a sports car than a jeep. And you don't have to worry about hydrolock unless your driving through a river. My car is barely off the ground(1-2 feet) and I drive with my cai in ANY type of condition. Now the cai pulls out cold air to the engine from the bottom. The air gets sucked in pretty close to where your left front tire would be. This makes it away from the engine compartment so it doesn't suck in hot air instead.

And yes, I think the whistling sound it makes and the swooosshh! sound it makes when sucking in sounds great. It's like a cargasm! lol.

I know this is a jeep forum, but here is a little vid of what my cold air intake sounds on my car:
You can't compare a ricer Tiburon with a Jeep 4.0L. Completely different purpose, different technology, different environments, different engine, different EVERYTHING. Go back to the first post and read the entire thread. You don't have a Jeep and you don't understand how they work, so don't add misleading information for the people who actually want to use this forum for a useful purpose.
 
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