FAQ - Cold Air Intake
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.
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).
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.
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:
1. Eliminates stock airbox (may be necessary for custom fenders)
2. Improved HP and TQ by about 2-3% at ~4500rpm (Engine max: 5200rpm).
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
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.
1. Introduces air from outside the engine compartment
2. Elevated air intake to resist hydrolocking engine during deep water crossings.
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/co...intake-860538/
Buick airbox mounted directly to the throttle body: http://www.jeepforum.com/forum/f9/i-...erated-863818/
Homemade snorkel with K&N: http://www.jeepforum.com/forum/f9/ho...w-pics-910113/
My personal favorites:
Windstar Airbox Cowl Intake: http://www.jeepforum.com/forum/f9/co...ir-box-566973/
Windstar Airbox Cowl Intake #2: http://www.jeepforum.com/forum/f9/wi...ntake-1064377/
Mustang Air box CAI: Mustang GT Air Cannister
Homemade Aluminum Snorkel: homebrew aluminum snorkel
$250 for a cold air intake system
- this will get you about 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:
STP paper filter cost from Autozone: ~$5
This means for the $250 the CAI cost, you could have bought 50 STP paper filters. Considering you can get about 6,000-9,000 miles from each paper filter, that means you could travel at least 300,000 miles on $250 of paper filters.
For the oiled filters, for the $20 for a K&N cleaning kit, you could travel 24,000 miles on paper filters.
For the cost of one CAI, and one cleaning kit, used to travel approx. 40,000 miles, you could travel 324,000 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.
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!
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:
Now we just need one for:
Throttle Body Spacers
Hi Lift mounts
How to increase MPG and power
K&N cleaning kit is 9.99. You get multiple uses out of it ;)
I documented my observations on the AEM Throttle body spacer and a 62mm bored TB here:
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.
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.
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.
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) ...
ARGH! What is the reasoning behind that?? They seem to work great?:confused:
"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."
Ok Boogieman...so then what in your opinion is the best solution when your engine is running a lil rough, assuming all fluids are where they should be and the oil is freshly changed...
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