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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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#247 ·
Thanks for the response, doublins. It'll be interesting to see how well it works when it's all put together. I think since you're running a stroker you might actually end up with something real.

PS Don't you love it when people make claims of increased horsepower AND better fuel economy when the only thing that changed on the engine is the intake tube?
 
#248 ·
Word!

I'm not actually expecting to achieve ambient IATs, but I do count on getting them down at least 40F at WOT.

Interestingly enough, my Z gets its air directly through the front grille and its IATs report as ambient, which is awesome. On an 86F day, I see 86F at the IAT sensor. If I can get anything like that through the cowl of the Jeep I'll be happy. Imagine how much less prone to detonation you are with 86F air vs. 150-200F air. At the top of the compression stroke, that 200F air is going to get HOT from adiabatic heating!
 
#249 ·
Well, I wrapped this up a couple of nights ago- did the old 3 1/8" hole saw through the firewall (hole went where the grounding bolt is, so I relocated said grounding bolt- I've only got my butt-dyno to go on and some 0-60 runs using my PLX Kiwi and software, as well as using the Kiwi to monitor IATs.

So... the results- take them for what their worth (or not worth)-

** Word of caution- do not exclude the possibility that part of these results might be attributable to the fact that I changed my air filter, period. Although, the stock air filter, which I changed when I dropped in my stroker in march, only had 4500 miles on it, but it was visually dirty.

1) Seat of the pants indicates a definite improvement, this is not a placebo effect or wishful thinking- there is a certifiable improvement in throttle response and acceleration, in particular from mid to upper range.

2) My best 0-60 as per the PLX kiwi/Rev dropped by about .4 seconds- from low-mid 8s to a best of 7.82- this was on a hot evening and last week when I took it out with the old airbox it was a bit cooler, so I might be able to get it down some. Same exact stretch of road, of course.

3) Highway acceleration in 5th is markedly improved- it had improved a LOT after the stroker build, but it has improved again after this mod.

No word on mileage, but I expect no improvement.

I'll post pics, but it looks just like the other windstar cowl induction jobs people have done.

-Chris
 
#250 ·
Oh yeah, and about the IATs- they're cooler on the highway by a lot, but after sitting, I believe that as the manifold heat soaks, the IAT sensor itself is actually heat-soaking, and remaining heated by the warm aluminum manifold, thus mis-reporting the actual air temperature of the air entering the engine. I am considering moving the IAT sensor to the plastic intake charge pipe itself just ahead of the throttle body, as I believe this will produce a more accurate IAT reading. This leads me to believe that the IATs with the factory air box are also not as high as reported by the sensor under WOT.
 
#251 ·
Oh yeah, and about the IATs- they're cooler on the highway by a lot, but after sitting, I believe that as the manifold heat soaks, the IAT sensor itself is actually heat-soaking, and remaining heated by the warm aluminum manifold, thus mis-reporting the actual air temperature of the air entering the engine. I am considering moving the IAT sensor to the plastic intake charge pipe itself just ahead of the throttle body, as I believe this will produce a more accurate IAT reading. This leads me to believe that the IATs with the factory air box are also not as high as reported by the sensor under WOT.
doublins

YOU ARE THE MAN!!!!!!!!!!!!!!!:cheers2: OUTSTANDING Job on this project. Your work is EXCELLENT! I am modeling an intake system for my 98 Wrangler using your work/project!!

Have you seen this post?

http://www.angelfire.com/my/fan/MAP_adjuster.html

Seems like an easy project for a little ECU adjustment amd some more fine tuning!!

Im going to give it a try and see if it will make any performance improvements.

BC
 
#252 ·
BC Jeep-

Thanks, but I can't take credit for this- all I did was copy another design I saw on here- I was just reporting back after doing it, but thanks for the props, lol.

About the map adjuster- I scored an old Apexi S-afc from a friend at a shop who had it laying around, figured out the wiring, and tuned it to zero out the fuel trims in closed loop, and added fuel as necessary for >70% throttle for open loop.

I had considered the map adjuster, but after looking at where I had to pull/add fuel, I don't think that a map adjuster would have made my ECU happy and provided the fuel I needed- it basically provides one blanket adjustment, richening or leaning, across all rpms, for all throttle positions- so, while it's probably better than nothing, I don't believe you could tune an obd-ii vehicle with it. Trust me, I looked into it, and based on my experience with obd-II cars (of which I've tuned several), I worry about it. In fact, I would only use a piggy back (like the s-afc) for simple naturally aspirated applications like my stroker- If I had any kind of forced induction or really heavily modded setup (high compression, etc)- I would use a standalone or at the very least the AEM setup.

I believe the map adjuster was probably a better option on the earlier-model vehicles.

Hope this helps!
 
#253 ·
Reported IATs after sensor relocation

So, yesterday afternoon, I relocated the IAT sensor from the manifold, to about 2" before the throttle body, and the difference in reported temps is night and day.

Yesterday it was in the mid-upper 90s here in MD, and after I did the sensor relocation, the IATs were reporting around 95 degrees if the jeep was moving at all, and about 110 if I sat and idled for a long time. By nighttime, after some storms came through and the temp dropped, I was seeing 78 degrees at the throttle body.

SO, what this tells me, is that there is little to no heating of the air drawn from the cowl via the intake tube- and that there is a major flaw with the placement of the factory IAT sensor- itś placement in the aluminum intake manifold directly above the headers causes it to heatsoak and mis-report the temperatures as being higher than they are.

The jeep is ready for the dyno, now, I believe.
 
#255 ·
I don´t remember- I ran a tap through the existing hole to figure out the size of the hole in the intake tube, honestly I matched it up and then just drilled and tapped without ever looking at what size tap it was. To plug the hole I had an extra manifold lying around from the block I´d bought to build my stroker, so I grabbed one of the extra plugs from there and screwed it in.
 
#256 ·
Glad to see some data supporting this mod as worthwhile (I was suspicious of how accurate some members' IAT monitoring methods were and didn't feel they were always a fair comparison ...not cowl in some cases and like you say, perhaps the heat soak of the actual body of the sensor when it's located in the manifold makes it less accurate). Personally I feel mine was very worthwhile since it didn't cost much at all by relocating the stock intake tube. I gained storage space for tools in the stock airbox and the new filter location is obviously better for water crossings. I find it very easy to believe I'm making another 5 - 10 flywheel HP at the peak ...and maybe a bit more even in the low and mid ranges but nothing substantial. It just feels quicker and sure as heck sounds more powerful lol, night and day on the sound anyway. I find less need to downshift and better high RPM breathing, doubt it's "all" in my head even though I know some of it is placebo butt dyno.

I'm not defending K&N as a good filtering product but I have yet to replace mine with a paper cone. Even after all this hoopla (lol esp in my thread) I'm considering keeping it . I can cheaply prefilter it by a variety of methods (panty hose on filter or even paper filter element wrapped around it with pleats intact ...not like my first pic of the temporary crap...already removed that as it was restrictive; also I'm already using additional window screen layers on cowl vent). I asked a knowlegeable engine building friend of mine what he thought about the "K&N debate" and this was his reply:

"I am familiar with the K&N controversy, and the empirical data
notwithstanding, here is my opinion.

Leave it on the Z, and take it off the Jeep.

The life expectancy of race engines will not be meaningfully affected by
a few more microns of dust. Your camaro is not opperated in a dusty
environment, the oil is always meticulously changed and of the highest
quality, and the motor will never see the high side of 50,000 miles
without a freshen if that.

The K&N flows well, and keeps anything meaninful out of the motor. The
jeep however runs for years and years and years in all sorts of road
conditions. It probably would see the measureable differnce in ring wear
over that many miles. I'm talking 150,000. Even then, I'd be surprised
if you could tell any performance difference due to additional wear. My
point is, just because you can find a 1 micron particle of something in
the oil doesn't mean it ever hurts anything.


I have run K&N's exclusively in everything I own (almost) for the last
20 years. The engines that I've taken apart after having run them were
spotless. Oil analysis may very well prove there are some additional
things present in the oil, but they're apparently too small to matter,
and are at any rate smaller than many other combustion by products
present in the oil.

FWIW, these are THE very best filters money can buy. Don't know if
they've got a fit for you though:"

http://www.r2cperformance.com/dirt-modified-filters.aspx

btw check out the filters he recommends in the link above, that sounds like the way to go ...I notice they have a "drag race cone filter" that I may consider for the cowl (again, removing it twice a year is no big deal to me). I found a cheap $7 purolator classic round filter that "almost" fit in the cowl. I'm considering using my K&N as a "base" and just wrapping the filter element from the purolator around it (with pleats intact) and zip tying. ...or ...prefilter with panty hose ....or .....simply buy one of the R2Cperformance filters from the link above and have peace of mind. Any of the above methods should be fine for my use (offroad only a few times a year).
 
#257 ·
I think the basic point is, if you can produce a free-flowing solution that takes air from the cowl, rather than underhood, and you re-locate your IAT, it´s a worthwhile investment of your time and effort.

My purolator filter & windstar box was cheap on ebay, the 4"->3¨ reducing elbow was $20, and relocating the sensor was free, and I am 100% certain that this has added power to my stroker.

When I dyno the thing, I´ll post here for $hits and giggles, but of course the last dyno I got was when the jeep was bone stock- now I have a 4.7L, aftermarket cam, oversized valves, cowl intake, header, and free-flowing exhaust, so I´ll have no way to say how much of a gain I got from just the cowl intake, all I can say is ¨my stroker with these mods made X more power than my stock wrangler¨

But, if you believe me, and I haven´t given you any reason not to, there is a worthwhile gain to be had with this mod. If it didn´t work, I´d have no problem saying ¨look, this is a waste of time.¨ Fortunately, it appears to be a worthwhile expenditure of time.
 
#259 ·
Hey does anyone run a Throttle Body Spacer with a Banks Intake on their 4.0L TJ? Will it make contact with the hood? I know that many manufacturer's intakes won't accomodate the TBS without modifying the tube, but I have not heard anything about that set-up with a Banks kit. Thanks for the help
 
#260 ·
A TBS should fit with the Banks CAI if you don't have a 1inch MML.
 
#262 ·
Not to mention the suck more crap in your engine too being most are oil based thats just a magnet for dirt. I bet any engine running a K and N or any filter like that with more than a few years of use the cylinder walls are scuffed pretty good from all the dirt that gets in not to mention the particules the oil has to deal with.
 
#264 ·
Actually if you use a pre-filter or have a Banks CAI the filter will stay just as clean as an OEM setup. I had an AFE CAI before the Banks and with the pre-filter I had no issues. I always check my tube for dirt since all the talk on here about how bad K&N type filters are and my tube is just as clean as with the OEM setup.
 
#265 ·
Today I sucked water in my CAI which i put one lnog before i found out they are completely useless. I probably would not have had the issue i had today with stock. So i am going to do cowl because the guys I wheel with do allot of water crossing. So I am thinking of going with the spectre filter box and using my cai tubing and some misc parts from oreily's to make a nice cowl intake. here is the filter box http://cgi.ebay.com/ebaymotors/?cmd=ViewItem&_trksid=p3984.m1438.l2649&item=370546282516&sspagename=STRK%3AMEWAX%3AIT#ht_1444wt_893
Any other boxes that would be better and or cheaper?
 
#268 ·
I will check around at the local junk yards. Are there any years that work the best?
 
#271 ·
FWIW I installed a Flowmaster super 44 offroad series muffler and and K&N Hi Volume kit. Last weekend I drove to Morgantown from my house(190 miles) and only used 3/4 of a tank with 35's and 4.10's. Before I put those on I made the same trip and only went 100 miles on 3/4 of a tank(I try not to go under 1/4 tank).

I don't care what anyone says about CAI's being snake oil.

The proof is in the puddin lol.
 
#272 ·
If you only went 100 miles on 3/4 tank of gas you had some serious problem with either or both of your intake and exhaust. You fixed it with the new parts, but no better (and maybe worse in the case of the KN) than stock replacment parts would have been. To give you comparison, on 33s with 3.73 I get regularly 200-220 miles out of 3/4s of a tank. Something was seriously wrong if you were only getting 100.

Also, personally I don't buy the stories about going below 1/4 tank being bad for your fuel pump (if that is the reason for you doing that). Regularly go down to 1-2 gallons in the tank and no fuel pump problems at 105,000 miles and counting.
 
#275 ·
Not that I believe the most recent CAI enthusiast's claim to magic Jeep milage and not to bust your balloon either..... but I do not use my Scanguage for gas milage. I have found it to be rather inaccurate for that. Mine right now is calculating my truck at 15.5mpg and actual is more like 12.5 based on fill ups and milage tracking. Over a tank that could be the difference between making it to your destination by Jeep or by foot :rofl:

Heavily modified Wranglers get 12-16 MPG real world milage and a muffler and CAI isn't going to change that. Mine has been consistent in regard to milage since new in 1998. Anyone claiming more either had alot of wind at their back, a big downhill, an anomoly tank or as a particular member here has, a special magic Jeep.
 
#276 ·
Heavily modified Wranglers get 12-16 MPG real world milage and a muffler and CAI isn't going to change that. Mine has been consistent in regard to milage since new in 1998. Anyone claiming more either had alot of wind at their back, a big downhill, an anomoly tank or as a particular member here has, a special magic Jeep.
lol, I check the average reading on a regular basis with ol' fashion calculations, and they come out within 0.5 mpg. the "instant" which is shown there is great for watching how much load is on the engine, and the delta is whats useful. you can train yourself to keep your foot out of it.

i can get between 13 to 18mpg on a regular basis....13-ish with more town & aggressive highway driving, 18mpg with all highway and mountains. in the mountains I get 5-8mpg uphill and 20-80mpg downhill :rofl: highway average is 16mpg, closer to 18mpg if i keep it under 60mph. I guess thats a benefit of the overly tall OD of the 42RLE. FWIW, my mom regularly gets 19-20mpg highway in her bone stock LJ w/ 42RLE (she does drive like an old lady).
 
#287 ·
I run the stock airbox system and paper filter. I'm of the crowd that feels it is plenty for the TJ and how I use it.

Something interesting though, I have long heard from many that the stock air intake flows more than enough for the 4.0.

I intalled a vacuum gauge for several reasons. A naturally aspirated engine when ran wide open throttle, with no intake resstriction will show no manifold vacuum. Above ~3800RPM it does start to pull a vacuum that increases until the rev limiter. Most noticeable when merging on the interstate and I shift around 5000RPM, or doing high(er) speed passing etc... it will pull up to 3inHg. Not the biggest deal, and an engine speed where the 4.0/Jeep isn't normally or often operated in, but interesting none the less. I installed a new air filter and it didn't make any changes - would be fun to play around with though and see what makes a difference.
 
#293 ·
I installed a new air filter and it didn't make any changes - would be fun to play around with though and see what makes a difference.
would you mind doing two other tests?

1. pull the horn off the stock box and run the test again.
2. shove a Ford Windstar fender horn into the opening of the horn, and push it up to the headlight like so:


Would be interesting to see what your vacuum gauge shows. Where is your gauge sensor installed?

my Scangauge II measures MAP (Manifold Absolute Pressure), and with the windstar horn + 62mm TB, it will peg @ ~12 psi @ WOT (i'm testing at 5000ft-12,000ft elevation, ~24in Hg). lower psi means more vacuum is drawn since absolute pressure at elevation is ~12psi/620mmHg/24inHg. meaning the computer thinks no vacuum is drawn. (for reference sea level is ~15psi/760mmHg/30inHg)

FWIW, this windstar horn setup with an otherwise totally stock box & tube has shown the lowest IAT's (Intake Air Temps). Tested AEM CAI, stock box with horn and without, stock box with a homemade heat shield, stock box/tube with header wrap, and a windstar box under the hood.
 
#288 ·
Rick

If your seeing a rise in vacuum without an air filter restriction, the only restriction that can cause a rise in intake vacuum is the Throttle Body. If minor TB opening porting and porting of the manifold directly below the TB doesn't improve the intake air flow, a larger TB would be the only resolution.

Does anyone know if there are any larger bolt on OEM Throttel Bodies that could be used on our manifolds??

Good info and excellent testing.:thumbsup:
 
#291 ·
Does anyone know if there are any larger bolt on OEM Throttel Bodies that could be used on our manifolds??
I had a stock TB bored to 62mm and a new butterfly installed. The opening on the manifold is 62mm, so I didn't see a reason to go to 63mm+ without porting it as well.

The Spectre kit and 62mm TB are working very well together.
 
#289 ·
BC Jeep said:
Rick

If your seeing a rise in vacuum without an air filter restriction, the only restriction that can cause a rise in intake vacuum is the Throttle Body. If minor TB opening porting and porting of the manifold directly below the TB doesn't improve the intake air flow, a larger TB would be the only resolution.

Does anyone know if there are any larger bolt on OEM Throttel Bodies that could be used on our manifolds??

Good info and excellent testing.:thumbsup:
There are 62 & 63mm throttle bodies on the market for a pretty penny. The stock air horn is a greater restriction than the TB though. It's only a 1.5" (close to that) opening. Try just taking it off first.

Where did you hook your gauge up to?
 
#290 ·
mike_dippert said:
There are 62 & 63mm throttle bodies on the market for a pretty penny. The stock air horn is a greater restriction than the TB though. It's only a 1.5" (close to that) opening. Try just taking it off first.

Where did you hook your gauge up to?
I'd like to see what formula you used to figure out how much air can flow through the stock horn.
 
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