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Old 11-16-2010, 12:33 AM   #1
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Cold Air Intake Debate

I'm an engineering student and i suppose when we have a question, we just figure it out with math so i used Excel to figure out what kind of advantage a cold air intake would have to have to make it worth it. From what I have read most people say they have little to no advantage in power gain or increased mileage but, that being said, it seems like they have to help somehow. They let more air in and at a lower temperature making it more dense, this means there is not only more air volume but more actual air particles and air makes up the majority of the combustion. Basically without beating this topic death more than it has already been beaten, if you can get 1 mpg out of a CAI, and it cost 250 dollars, and you spend $1 per 30k miles on maintaining it as opposed to spending $5 per 30 k miles on a new paper filter it will pay for itself in fuel savings in just under 22K miles. If any of you have more specific numbers, i can try to send you my excel or put your numbers in my excel and see what it spits out. This is assuming $2.73 per gallon and it is also assuming that the filter does not have any ill effects on your engine, like letting it get dirty, which would cost money to fix later. I know the beef a lot of people have with CAI filters is that they don't clean the air. I dont have one so i wouldn't know. This 1 mpg increase is also arbitrary and i dont know if thats way to high or not. Let the debate ensue.


If you dont like to read ...
CAI: $250
gas 2.73 / gal
CAI Maintenance $1/ 30k miles
Paper filter $5 / 30k miles
Cai pays for itself in 22k miles

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Old 11-16-2010, 05:51 AM   #2
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"They let more air in and at a lower temperature making it more dense,"

Your theory has some issues

- Your engine is an air poump. Each pistion as it on the down cycle will pull in a fixed voulume of air. A CAI is not going to let any more air in. Where a high flow filter CAN be effective, assuming IF the stock system and filter is restrictive, the engine will not have to work as hard (use more power) to draw in the fixed volume of air.

- Most of the "CAI" are NOT cold air indictions. Look at most of the TJ kits. They place the filter right where the stock intake was to start with. Yes cold/cooler (from outside the engine area) will be more dense and have some potentenial for making a tiny bit more power but it needs to be from OUTSIDE the engine area. For a lot less than the 250 for K&N and others, you can make an intake using the stock air filter box or other boxes people have adapted and plummed them to pull from the cowl area which receives direct outside air. If you want it the Spectre Air kit cost a lot less than 250 and goes to the cowl.

- With the pressure vehicle manufactuers to make CAFE standards, if it were so easy to increase 1 MPG, the vehicle manufactuers would be doing it. You are not going to get 1 MPG out of it.

- It may not be you but many people state they want MPG and HP from mods like this. To test or flog their possible HP, they will romp on the go pedal more. Those romps totally blow any MPG gains over the long run.

- Lets leave the debate of K&Ns and others not being proper for off road dust and dirt out of this thread.

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Old 11-16-2010, 08:15 AM   #3
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Quote:
Originally Posted by CRolandLJ View Post
I'm an engineering student
...

CAI: $250
gas 2.73 / gal
CAI Maintenance $1/ 30k miles
Paper filter $5 / 30k miles
Cai pays for itself in 22k miles
You need to learn to do math better if you're going to get through engineering

For the $250 it cost you for the CAI, you could have traveled 300,000 miles on paper filters, assuming they cost $5 each - and thats changing the filter every 6000 miles.

Quote:
Originally Posted by Unlimited04
Cost Effectiveness:
$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.
from here: FAQ - Cold Air Intake - JeepForum.com

Also, when i ran a cold air intake, I saw a DROP in mpg. The filter clogged every few weeks, and the engine idled at 1000-1200 rpms, until cleaned. The throttle body was very dirty, and the intake tube actually had fine grain sand inside it, which had been sucked through the CAI.

On top of that, a CAI is still sucking air in from the same hot underhood area your stock box is. If you really want a true cold air intake, you'll need to cut a hole in your firewall. Pipe in a Windstar airbox for $20 in junkyard parts, run a Wix or AC Delco paper filter and you get good filtering, cheap price, and truely cool air sucked in from outside the engine compartment.
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Old 11-16-2010, 08:36 AM   #4
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Suppose one could always remove the air filter altogether on a foggy day, replace it with a screen to keep any mice from finding their way into the throttle body, and go for heart throbbing acceleration and superior gas mileage. Just kidding.

In the days of carbureted engines giving the engine more air, through less restrictive air filtration, meant something.

What does it mean for computer controlled fuel injected engines in use today? Not that much apparently. Here's an interesting article called 6 Gas Saving Myths.
Quote:
Myth #2. Change your air filter
Maintaining your car is important, but a clean air filter isn't going to save you any gas. Modern engines have computer sensors that automatically adjust the fuel-air mixture as an increasingly clogged air filter chokes off the engine's air supply.

While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.
So ........ save your $, and possibly your engine, by sticking with the stock setup which provides the minimum degree of filtration needed for your engine. Anything else is likely less than minimum. Also keep in mind that as the air filter (oil filter as well) collects dirt, it becomes more restrictive and thus becomes a better filter (up to a point).

After all is said and done, the overarching objective is to keep dirt out of the engine through adequate filtration. Less isn't best.
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Old 11-16-2010, 10:18 AM   #5
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Ok well I can do math and I didn't assume $5 every 6k miles. If it doesn't help mileage then this is a moot point anyway. And I understand how an engine works and by more volume I meant more volume flow rate which I should have indicated meant easier work for the engine. I also didn't know the tidbit about cai not relocating the intake. It seems rather stupid So basically they are a waste of money
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Old 11-16-2010, 10:42 AM   #6
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Originally Posted by CRolandLJ View Post
Ok well I can do math and I didn't assume $5 every 6k miles. If it doesn't help mileage then this is a moot point anyway. And I understand how an engine works and by more volume I meant more volume flow rate which I should have indicated meant easier work for the engine. I also didn't know the tidbit about cai not relocating the intake. It seems rather stupid
the thing is the air intake only has to flow as much air as the engine can use at maximum RPMs at wide open throttle. The 4.0L flows about ~385 cfm at WOT @ redline. The stock airbox (with mini-snorkel horn removed), and throttle body, actually flow more than that. but who drives a WOT @ redline all day?

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So basically they are a waste of money
now you're catching on!
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Old 11-16-2010, 10:44 AM   #7
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They sound cool
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Old 11-16-2010, 10:51 AM   #8
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Quote:
Originally Posted by UnlimitedLJ04 View Post
The stock airbox (with mini-snorkel horn removed), and throttle body, actually flow more than that. but who drives a WOT @ redline all day?
Is it a bad thing if I raise my hand???
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Old 11-16-2010, 11:22 AM   #9
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They let more air in and at a lower temperature making it more dense, this means there is not only more air volume but more actual air particles and air makes up the majority of the combustion.
This is exactly the argument I've been making for cold air intakes. On sports cars, and I use the term loosely, a CAI is routed through the front bumper, pulling up cold air (which is at the bottom since heat rises) as it is sucked up into the bumper. The Jeep CAI (really short ram intakes), are pulling in air at the same location as the stock so there isn't any temperature benefit.

There's no reason for Jeep to have made a restrictive air box. It's hard plastic now and it's a fuel injected engine. The 4.0L is more then loud enough on it's on.
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Old 11-16-2010, 11:35 AM   #10
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If you want cold air intake, just move north and add a little salt dust to flavor it.

Beware of wolves in sheeps clothing. What damages your engine more, the dirt contained in the oil that lubricates it, or the dirt contained in the air that it breathes? Did somebody say "dirt in the air"?
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Old 11-16-2010, 12:09 PM   #11
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So if i take off that snorkel horn thing it will help my mileage and power?
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Old 11-16-2010, 12:45 PM   #12
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So if i take off that snorkel horn thing it will help my mileage and power?
No. Don't you think Jeep engineers would have thought of that?
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Old 11-16-2010, 12:55 PM   #13
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I love how many of these cold air intake threads there are. So what the heck I'll throw in my .02 I ran a k&n intake on my f150 for 4 years, did it increase power I'm not sure but it did increase throttle response and maybe a mpg or 2 but with the way I drove it I couldn't tell. Not saying same will happen on a jeep as I don't have one on mine at the moment. In those 4 years I cleaned the filter twice and before I sold the truck I pulled off the intake tube and the inside of it and the throttle body were as clean as when I installed them so I dont get the whole letting dirt in but hey that's just my experience with them over 4 years driving my truck everyday
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Old 11-16-2010, 12:57 PM   #14
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I love how many of these cold air intake threads there are. So what the heck I'll throw in my .02 I ran a k&n intake on my f150 for 4 years, did it increase power I'm not sure but it did increase throttle response and maybe a mpg or 2 but with the way I drove it I couldn't tell. In those 4 years I cleaned the filter twice and before I sold the truck I pulled off the intake tube and the inside of it and the throttle body were as clean as when I installed them so I dont get the whole letting dirt in but hey that's just my experience with them over 4 years
There are plenty of people who have run the K&N filters on their Jeeps here on the forum that will attest to how much dirt they found inside their intake tube after installing the K&N.
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Old 11-16-2010, 02:01 PM   #15
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There are plenty of people who have run the K&N filters on their Jeeps here on the forum that will attest to how much dirt they found inside their intake tube after installing the K&N.
That's fine ill attest to how clean mine was everyone has an opinion just giving mine
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Old 11-16-2010, 02:20 PM   #16
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But there is one more thing that ALL of you have forgotten. The fact that Chrysler wants to charge $400 for a new stock air box for a TJ! When I need one because the original was warped and couldn't filter a boulder they told me I had to buy the entire kit (piping and all), not only that but it was going to take 3-4 weeks to get here. I don't know about you but from where I come from TJ's don't usually make it to the wreckers and even if they do they are picked clean swiftly, then the parts are sold off at a premium damn close to what a new part with a warranty would be. That's of course if you can find the parts in the first place. So $250 for the Airaid CAI that I got, with the 3 stage handmade lifetime warranty filter and prefilter was a wicked deal compared to what the dicks at the stealership were trying to take me for. I have had it on the Jeep for 3yrs now and I have NO complaints, No dirt has been ingested. I don't speak for the quality of all CAI's just the Airaid.
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Old 11-16-2010, 02:26 PM   #17
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That's fine ill attest to how clean mine was everyone has an opinion just giving mine
Noted. Your experience was with a K&N on an F-150, so your opinion may be more applicable to an F-150 forum, but otherwise duly noted.
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Old 11-16-2010, 02:37 PM   #18
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The fact that Chrysler wants to charge $400 for a new stock air box for a TJ!
....
So $250 for the Airaid CAI that I got
...
was a wicked deal
Ford Windstar airbox for $15 from the You-Pull-It, $6 in hose clamps & JB Weld from ACE hardware, $12 for elbow and reducer from Intakehoses.com gives a grand total of $33 for a true cold air intake, using a paper filter for maximum filtration.


but oh...are you a little gunshy about cutting a hole in your firewall, and too lazy to figure out how to flip the windstar box around?

then use a Buick airbox for $15 alone!


theres also the Mustang GT airbox:


Ok, now how is a CAI cheaper again?

But if you're not into the junkyard thing, you can always buy the MCAI from SkinnyPedal
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Old 11-16-2010, 02:49 PM   #19
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why would you put the intake of the COLD air intake over the HOT engine? Just a question, it doesn't make sense to me.
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Old 11-16-2010, 02:59 PM   #20
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Chrysler had to consider the noise factor when they designed the stock system. There are Federal limits as to how much noise can be emitted from an engine - actually the entire vehicle. If it doesn't meet the standards, they can't sell it. Same thing with smog emissions.

The stock airbox and the tiny little funnel in front acts as a muffler to lower the noise emissions. They had to make a trade off between performance and not selling them in the US.

At lower speeds it's not restrictive, but the faster the engine turns the more air it needs, and the stock system becomes more restrictive.

Try something - simply remove the tiny funnel - then drive it - notice it makes much more noise.

Now put on a low restriction system - even more noise.

Of course when the air is reduced due to restriction, the PCM just cuts back on the fuel to keep the AF ratio at Stochiometric. But at the higher R's where the air becomes limited, the entire fuel/air charge is smaller - limiting power.
At medium higher speeds to get the same power the throttle has to be open farther than if no restriction. As we all know, the 4.0 driving the non aerodymic "brick" is under powered anyway. So on hills or a headwind you need all the power you can get. This means you usually run at large throttle opening.

At WOT the computer just goes full rich, hoping there's enough air available.

Most of the so called "cold air" systems really don't bring in colder air, and if it did, the temperature difference is slight.

Try it - use a remote thermometer in the airstream to see if there's much difference.

Had to laugh - a previous post said something about since it's fuel injection, it doesn't need as much air.
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Old 11-16-2010, 03:13 PM   #21
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I ran the AEM brute force, it pulls air from under the hood, not a real CAI, but I liked it, felt a good diff. I don't care what people say and what infor they have from a book, I felt a diff. I switched to a canister type cone filter that I put inline with an ARB snorkle (True COI) and lost power (Plus added a big hole in the fender to mount the thing). Refering to saving gas, you won't, you could but you won't. The little bit of gass you could save will be a victum of the new peppy(er) ride and your right foot and skinny pedal. To summarize, AEM Brute force = good, ARB Snork = Bad (For DD).
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Old 11-16-2010, 03:24 PM   #22
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No. Don't you think Jeep engineers would have thought of that?

Maybe Jeep engineers were more concered with keeping water out or something. Or maybe they thought about it but decided to keep it for some other reason. Sometimes they have other motives for doing that. They arent necessarily trying to build the most fuel efficient, powerful car ever, they are trying to build a car that a lot of ppl will buy and make it as cheap as possilbe while still being reliable and bringing the buyers back. I was just saying that the impression i got from a previous post was that with the snorkel horn off, it provided more flow.
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Old 11-16-2010, 03:45 PM   #23
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Despite all the hate for CAI they have some use but only after you have upgraded your headers and exhaust to flow better first. But thats only if your jeep is a DD and dosent see much offroad and you already upgraded the exhaust. I personally want to get a AEM bruteforce after i get my banks catback but would put my stock box back on before i go offroading. Too much crap gets in the engine bay when offroad and the CAI is only going to benefit at the really high rpms with a power increase, its not guna change your gas mileage because at low rpms the stock flows enough air to get the job done.
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Old 11-16-2010, 04:54 PM   #24
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why would you put the intake of the COLD air intake over the HOT engine? Just a question, it doesn't make sense to me.
Why do companies sell things call cold air intakes, when they route a metal tube over the HOT engine, when the metal serves like a giant heat sink to actually increase the intake air temperature?

Chrysler piped the intake over the engine from the factory...but they used a plastic tube that resists heat soak somewhat. Lots of auto manufacturers pipe the tube over their engines. Besides, if you get a OBDII scanner and watch the intake temps via the IAT, you'll actually see the tube over the engine has little effect. Your IAT temps usually don't deviate from ambient a whole lot on the highway. I've seen roughly twice ambient temps as the norm, and at the worst around 180 deg F idling in traffic on a 100 deg day. The more you get on the throttle, the lower the intake temps...obviously since you're sucking in more air. If you keep the throttle blade closed, the air has time to heat up...both in the manifold and the tube.

There are far more heat soak issues from the aluminum intake manifold itself being directly above two cats (on 2001+) operating at ~600+ deg F. Ever get heat soak causing rough idle on startup? Thats the exhaust causing enough heat soak through the manifold to actually vaporize the fuel in the fuel rail. You end having to floor the gas pedal to get to WOT in neutral, so the vaporized fuel can be cleared by the injectors. Theres a TSB on that...

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but only after you have upgraded your headers and exhaust to flow better first.
See thats the problem - the stock 4.0L already has plenty of breathing room. Its been hot-rodded from the factory as much as it can be for the tractor motor that it is. In the TJ series, the accesories are already capable of flowing more air in and out than it can use stock. Now if you bore it out, port the heads, stroke it, run a hot cam...you've increased the volumetric efficiency and the bolt ons can start to make a difference. Otherwise not so much. But how many people are actually willing to run a hot cam? pull the radiator, condensor, half the front and the head to install a $300 cam & new valve springs & rockers...so they can notice a difference from their $300 header?
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Old 11-16-2010, 05:05 PM   #25
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Originally Posted by UnlimitedLJ04 View Post
Why do companies sell things call cold air intakes, when they route a metal tube over the HOT engine, when the metal serves like a giant heat sink to actually increase the intake air temperature?

Chrysler piped the intake over the engine from the factory...but they used a plastic tube that resists heat soak somewhat. Lots of auto manufacturers pipe the tube over their engines. Besides, if you get a OBDII scanner and watch the intake temps via the IAT, you'll actually see the tube over the engine has little effect. Your IAT temps usually don't deviate from ambient a whole lot on the highway. I've seen roughly twice ambient temps as the norm, and at the worst around 180 deg F idling in traffic on a 100 deg day. The more you get on the throttle, the lower the intake temps...obviously since you're sucking in more air. If you keep the throttle blade closed, the air has time to heat up...both in the manifold and the tube.

There are far more heat soak issues from the aluminum intake manifold itself being directly above two cats (on 2001+) operating at ~600+ deg F. Ever get heat soak causing rough idle on startup? Thats the exhaust causing enough heat soak through the manifold to actually vaporize the fuel in the fuel rail. You end having to floor the gas pedal to get to WOT in neutral, so the vaporized fuel can be cleared by the injectors. Theres a TSB on that...
Thanks, I don't have those kind of toys... just thought it would be a strange set up, but you explained it well.
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Old 11-16-2010, 05:48 PM   #26
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Much to do about a little air and what happens at high rpms (in a Jeep Wrangler???). Considering I don't take the Jeep to the drag strip and a head wind hitting the equivalent of a brick wall, is going to slow me down regardless, I can't see myself hooking up a "wishful thinking" air intake. I wash my Jeep and it will have more power, ride better, and be much quieter - works for me.

On a more serious note, JP Magazine tested several air intakes and reported on the tests in its February, 2009 issue. Here's a twist.
Quote:
Sometime between the last test and this one, we had formed a working theory that it wasn't so much the air filter as the air tube that makes the power in these kits. With most, if not all, aftermarket air intakes, the air filter itself can flow more air than the Jeep can use. Sure, there are varying degrees of restriction from one filter to the next, but on a stock 4.0l engine we just aren't convinced that a significant result will be seen at the wheels from the air filter alone.
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Old 11-16-2010, 07:38 PM   #27
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Noted. Your experience was with a K&N on an F-150, so your opinion may be more applicable to an F-150 forum, but otherwise duly noted.
As far as power/mpg I cant say that on a jeep which I stated, as far as a dirty intake I can. Mine being clean after 4 years with no issues, I dont really understand how other peoples are dirty, I drive the same roads as jeeps do and I took it through some fields and in the dirt from time to time so something doesn't add up there. Mine filter sat right in the enginebay as a jeeps would.
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Old 11-25-2010, 02:05 AM   #28
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I've been running a cold-air intake system on my last two vehicles. My last vehicle was a Dodge Ram 1500 with a 4.7 V8. The AFE stage 2 helped it immensely and sounded like a hemi.

My current ride, an 08 Rubicon Unlimited is running with a stage 2 AEM and I noticed the improvement as soon as I bolted it on. Excellent throttle response and great sound. Combined with the throttle body spacer and hypertech max energy, I'd like to think I'm getting more power and better fuel economy. I'd rather not hear the opposite. Lol! Who cares really? If you're happy with the gains, to hell with the spoilers that want to say different. Drive and be happy! If I was that concerned about saving money....jeep would be my last choice in vehicles..lol!
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Old 11-25-2010, 02:17 AM   #29
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Quote:
Originally Posted by Rubiconwarrior View Post
I've been running a cold-air intake system on my last two vehicles. My last vehicle was a Dodge Ram 1500 with a 4.7 V8. The AFE stage 2 helped it immensely and sounded like a hemi.

My current ride, an 08 Rubicon Unlimited is running with a stage 2 AEM and I noticed the improvement as soon as I bolted it on. Excellent throttle response and great sound. Combined with the throttle body spacer and hypertech max energy, I'd like to think I'm getting more power and better fuel economy. I'd rather not hear the opposite. Lol! Who cares really? If you're happy with the gains, to hell with the spoilers that want to say different. Drive and be happy! If I was that concerned about saving money....jeep would be my last choice in vehicles..lol!
Not trying to poke BIG holes in your story bud but ...the JK's 3.8 V6....is NOTHING like the 4.0L straight six. You will see better gains on yours. The 4.0L straight 6 is an OLD OLD design and see's no benifet from Air intakes. I've tested many different intakes over *cough* a decade....I've never produced any gain from the intake on a 4.0 but I have seen it decrease on 3 products.
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Old 11-25-2010, 03:49 AM   #30
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I just ripped mine off and put a pair of my wife's panty hose over the TB. Works great and it was free.

Happy Turkey Day Everyone

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