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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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#45 ·
Some good info, thanks.
 
#50 ·
One thing I like about a high flow filter, is the increased throtle response, instead of the delay. My brother has a CAI on his 2000 TJ, and I have the stock air box on my 05 Rubi, and the throttle response sucks on mine. I dont race nor do I hot rod but the delay when you give it gas is so annoying and doesnt feel like a normal vehicle like my brothers does when you accelerate.
 
#54 ·
Dippert, the TrueFlow air filter seems to be a pretty good one. I dumped my K&N with two prefilters over the top of it in favor of the TrueFlow and it seems to be filtering pretty well. I put both of my prefilters over the top of the TrueFlow rather than trash them, I believe my engine is finally getting some clean air. I didn't notice (nor did I expect) any throttle response difference. :)
 
#67 · (Edited)
What About Mopar Perfomance CAI?

OK, so what about the OEM CAI and Filter from the MOPAR performance catalog (http://www.mopar.com/performance/trail/coldairintake/index.html). The performace catlog (http://www.moparsupercenter.com/mopar-performance-catalogp5153859.html) list the P/N as: 77060081 Cold Air Intake System, Dry Filter, 2007-09 Wrangler
;) NOTE: I have an '09 JK.
Runs $316 at http://www.wholesalemopar.com/parts_catalog-small.html?gclid=COCK7Mqc_pkCFWVM5QodAx5_FQ
So is this a waste of money? If so, why does Mopar Performance advertise it as a HP add bolt-on?
 
#68 ·
OK, so what about the OEM CAI and Filter from the MOPAR performance catalog (http://www.mopar.com/performance/trail/coldairintake/index.html). The performace catlog (http://www.moparsupercenter.com/mopar-performance-catalogp5153859.html) list the P/N as: 77060081 Cold Air Intake System, Dry Filter, 2007-09 Wrangler
;) NOTE: I have an '09 JK.
Runs $316 at http://www.wholesalemopar.com/parts_catalog-small.html?gclid=COCK7Mqc_pkCFWVM5QodAx5_FQ
So is this a waste of money? If so, why does Mopar Performance advertise it as a HP add bolt-on?
You obviously need to read the first page again because something didn't sink in.
 
#70 ·
So, were you born a cynic, or has only just recently come naturally to you? Yes I read the page, let me be more concise...cai is dyno tested to add horsepower and torque not to mention improved mpg. This is fact not fiction! It is one of the few cost effective simple bolt-ons the average joe can perform. My point is, mopar performance would not sell you something that does not meet it's claims! Where else, praytell, can you spend a two or three c-notes and in about an hour have added 6 to 15 HP and 25 ftlb of torque? That's money well spent in my book.
 
#72 ·
So, were you born a cynic, or has only just recently come naturally to you? Yes I read the page, let me be more concise...cai is dyno tested to add horsepower and torque not to mention improved mpg. This is fact not fiction! It is one of the few cost effective simple bolt-ons the average joe can perform.
You will see no noticable HP/TQ or mileage increase, unless you drive at 4500-5000rpms. Sorry.

My point is, mopar performance would not sell you something that does not meet it's claims!
OHHHH YES THEY WILL.

Where else, praytell, can you spend a two or three c-notes and in about an hour have added 6 to 15 HP and 25 ftlb of torque? That's money well spent in my book.
You're way off on your figures. 3% improvement in HP, according to magazines...so like 4-6hp and 4-6 ft-lbs, and at 4500-5000rpm. When's the last time your Jeep saw 4500rpms? And when's the last time you got a mileage improvement by driving at 4500rpms? Btw, my mileage went DOWN with an AEM/MOPAR CAI.

Oh, if you'd read the first page then you'd know you can travel about 200,000 miles on paper air filters for the cost of that $300 CAI kit.
 
#76 ·
All I know is from firsthand experience, I had a 1996 VW Passat VR6 with a Neuspeed P-flow and a K&N air filter on it; and whereas I did "feel" better acceleration and get better gas mileage from the car compared to my wife's nearly identical 95 VW Passat VR6, my car also threw CELs all the time where her's did not! I had to replace the MAF sensor several times (which sits right behind the K&N).

I would have to be a total idiot to run a K&N air filter on my LJ down here in dusty central Texas! All you have to do is look at the filter to realize it doesn't stop small particles from passing through it! The stock airbox and filters I use stop a lot of crap from getting into my engine, and the 4.0 I6 is pretty much bulletproof if you take care of it. Why screw up a good thing for a little temporary gain on an engine that was designed more for torque that acceleration?!?
 
#77 ·
All I know is from firsthand experience, I had a 1996 VW Passat VR6 with a Neuspeed P-flow and a K&N air filter on it; and whereas I did "feel" better acceleration and get better gas mileage from the car compared to my wife's nearly identical 95 VW Passat VR6...
How does a K&N Filter help with better gas mileage?
 
#82 ·
Probably can't. Even a bigger throttle body probably won't work. Cold air works. Not much, but in my case 1-2 mpg improvement.
 
#86 ·
You made a post that extolled the virtues of CAI setups and claimed them as beneficial. To come back after the fact and say duh you obviously weren't saying they're useful on Jeeps everyone knows that blah blah blah, well... If we give you the benefit of the doubt, must assume that you're just a terrible communicator. Otherwise, it's nearly trollish.
 
#98 · (Edited)
Nice find. Interesting to play with the numbers. According to that calculator, the 4.0L's stock throttle body is not a limitation - even at WOT, and is capable of supporting more than the stock engine itself is even capable of making.

Assuming 80*F intake temps (175*F) as a worst case scenario:
- At 5200RPM, with the stock 58mm throttle body you get 319.53 CFM and 196 HP.
- At 5200RPM, with a 63mm throttle body you get 319.53 CFM and 196 HP

Assuming 20* F intake temps (68*F) as a best case scenario:
- At 5200RPM, with the stock 58mm throttle body you get 319.53 CFM and 236.2 HP.
- At 5200RPM, with a 63mm throttle body you get 319.53 CFM and 236.2 HP

The 4.0L itself is rated at 190 HP - thats measured on a dyno, at the crank, in a lab! This math confirms no matter what throttle body you have, you get the same power. It also confirms the Jeep's intake capable of supporting more power than the engine itself is even capable of making.

Throttle body spacers - you can play with the throttle body bore depth to see the possible pressure difference due to throttle body length. You get the same value - 0.22 psi @ 20*F - for 1", 2", 3" and even 10" with the stock 58mm throttle body. For 80*F, the result is a 0.18 psi pressure drop, regardless of intake length. With a 63mm throttle body you get 0.16 @ 20*F for 1" and at 10" you get 0.16 psi. For 80*F, the result is a 0.13 psi pressure drop, regardless of intake length.

This shows what most here already know - throttle body spacers are useless, whether the TB is 1" or 10" high!! It does show slightly less pressure drop with a 63mm vs stock 58mm TB, resulting in 1.2 hp less drop in power - @ 5200 RPM with 68*F intake temps.

So best case scenario - a 63mm TB will allow you to save 1.2 hp @ 5200 RPM, assuming you have 68*F intake temps.
 
#100 ·
Wow... some very strong opinions... wouldn't it make a difference on where you live? Meaning, altitude, temp during the winter and summer months...what may work for someone in CO or the upper east coast may not work for someone who lives in the south or even on the west coast?
 
#101 · (Edited)
Wow... some very strong opinions... wouldn't it make a difference on where you live? Meaning, altitude, temp during the winter and summer months...what may work for someone in CO or the upper east coast may not work for someone who lives in the south or even on the west coast?
well there are three constant items in case you weren't paying attention.

1. Dust - open element air filters allow a lot more dust into your engine
2. The stock intake flows plenty of air - it was specifically designed to be non-restrictive.
3. an open element air filter under the hood sucks in the same air the stock intake does.
 
#102 ·
Yeah, taking a hard look at my Banks

I installed the Banks on my TJ late spring, and have had doubts all
summer. The summers here in the Vegas valley are a pizza oven.
I know, that big opening on the filter housing is just sucking in a lot of
extream heat and all trails out of here are heavy dust.
good thing I still got the original air system, I'm putting it back.
See how she runs. Live and Learn.:cheers:
 
#106 ·
groundhounds cai concept

I was at that site you sent, That would seem fine on the street(no dust)
but out here in the desert with the intense dust, but then most of the dust
is kicked up behind the vehicle on the trails, I think it's worth the try.
I'm retired, so I got lots of time for this sort of thing, goofey or not.:2thumbsup:
 
#107 ·
I can't help it but, when I see words like "K&N", "RP", "Amsoil" and "Fram", I just have to say to myself that these are free thinking consumers and they are entitled to their beliefs. I hope that they respect mine.
 
#108 ·
I bought the edge kit for the 4.0 (back when it was still close to a grand, but I was young, and didn't know how to work on cars so it was good starter). This was on my 01 DD xj, it comes with an AEM CAI, 62 mm throttle body, and a programer. I didn't get a chance to test the products individually however there was a considerable seat of the pance feel in power and highway driving was considerably easier. However, I've learned that MPG improvement that the manufacturers claim are bold face lies as the whole kit was advertised to give you another 2+ MPG. The best I've ever done with stock tires on it was 24 mpg which is good for the XJ but that was fueling up, getting right on the highway for a straight 320 miles. But around town there was no difference mileage. I put that on about 4 yrs and about 50,000 miles ago and haven't cleaned the filter yet but have never off roaded it.

I did replace the stock paper filter in my 98 v6 s10 with a K&N, again a very very slight seat of the pance feel but no increase in MPG. And the oil absolutely played havoc with the air system as these trucks have a Mass airflow sensor that got clogged up and caused a CEL light. When I replaced the engine (knew a little more about working on cars at this point ;)) I cleaned the sensor and went back to a paper filter.

I'll maybe never buy another CIA kit again cause like every one else alludes to they just aren't worth the money. I've heard limited success with people making their own for less than 45$ so that may be the way to go, if I ever manage to get my wrangler back in one piece that is :rolleyes:.

Just thought I'd chime in on an old but great thread.
 
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