CAI Are Bad News!!!!!!!!

I've linked this thread numerous times:

http://www.dieselbombers.com/chevro...rticles/16611-duramax-air-filter-testing.html

 

Here is a good article on aftermarket air intakes I read that talked me out of buying one for my Subbie STI and my Tacoma. I know the article is for turbocharged subbies(which is a high performance vehicle compared to the tacoma), but I always go back and re read this when I even start to think about purchasing a CAI for any vehicle I own.



Overview
As long as people have been modifying their vehicles for improved performance, one basic upgrade philosophy has always remained constant regardless of the model -- replace the restrictive factory intake air cleaner system (aka air box). This simple modification has been a proven way to easily and safely improve the performance and sound of your vehicle's engine. As modern vehicles get more complex, however, this once infallible upgrade path needs to be reevaluated.
In this technical article we are going to discuss the type of intake air cleaner system used on the 2002+ factory turbocharged models from Subaru, the potential problems that might arise from modifying it, and potential solutions.
Please note that the content of this technical article is specific to 2002-newer Subaru factory turbocharged vehicles including the WRX, STi, Forester XT, Baja Turbo, and Legacy GT Turbo/Outback Turbo. The systems used on other year models and non-turbo versions do differ in design and the information included here does not apply.
Intro to the Intake Air Cleaner System (aka Air Box)
The factory intake air cleaner system is designed to work as a complete system to provide a steady supply of filtered, cool air to the engine. A large emphasis is also placed on maintaining an acceptable induction noise level that enters the passenger cabin. Believe it or not, not everyone wants to hear the roar of the engine under acceleration or the whine of the turbo. The goals of the engineers at Subaru include, among other things, proper power generation with a low induction noise and a consistent air intake charge and temperature.
The components that make up the factory intake air cleaner system are:

• Air Intake Duct
• Air Resonator Box (in fender)
• Upper and Lower Air Cleaner Cases
• Paper Style Air Cleaner Element

All these items are what are typically replaced when changing the system out for an aftermarket unit. The most common configuration is to replace all these components with a metal pipe that has a conical style filter element attached at the end. Filter placement is either located inside the engine bay or in the inner fender well where the factory Air Resonator Box normally resides. Systems with filters located in the engine bay are normally marketed as Ram Pod or Short Ram intake systems. As underhood air temperatures are normally quite higher than ambient temperatures, we will herein refer to this style of intake as a hot air intake. The systems with the filter located in the inner fender well are normally marketed as Cold Air intakes, as they reside in the cooler wheel well.
How it works
One critical design feature of this system, which differs from those used on most other vehicles, is the installation of the Mass Air Flow (MAF) sensor into the Upper Air Cleaner Case - instead of its own housing which has been traditionally the case with MAF equiped vehicles. It is primarily due to this design feature that problems may arise from modifying the factory air cleaner system.
When changing the factory air cleaner system out for an aftermarket system, you are required to relocate this MAF sensor into the new system. Due to this relocation, we have now opened up the potential for problems to occur.
The Mass Air Flow (MAF) sensor is a critical sensor used by the engine management system. The job of the MAF sensor is to monitor the Mass of air that is entering across the intake system. This is important because all of the fuel, timing and other critical engine management decisions are based primarily on what the MAF is reading. If this reading is off, then so will the fuel, timing, etc which has the potential to cause poor driving conditions or worse, engine damage.
Potential Problems caused by Aftermarket Intakes
MAF Sensor Housing Size
The MAF sensor only samples a small portion of the air coming into the system. From that sample measurement, the engine management system can calculate how much air is actually entering the system because it knows the inner diameter of the MAF sensor housing it is sampling from.
If the MAF sensor housing inner diameter changes in any way, the calculation performed by the engine management system will be incorrect. This means that the amount of air actually entering the system will be different from what the computer thinks is entering the system. This is critical because the computer determines how much fuel and timing to run based on this value of air. When it's wrong, it can cause the engine to run richer, or leaner, than it should.
With aftermarket intakes, it's extraordinarily common for the piping used to have a different inner diameter than the MAF sensor housing incorporated in the factory air box. This is due to the fact that the exact inner diameter of the factory MAF sensor housing is different than what's commonly available in the standard metal piping used for aftermarket intake systems.
It is true that some aftermarket intakes show an increase in power when installed on a stock vehicle. This power increase is due to the fact that the aftermarket intakes have a larger inner diameter for the MAF sensor housing to mount into which in turn leans out the Air/Fuel mixture because of this error in calculating how much air is actually entering the system.
Please note this is NOT due to the fact that the aftermarket intake is so much less restrictive than the stock air box and therefore more air is getting in but rather that the computer does not know it's now sucking from a larger tube and therefore more air is getting in.
So to recap, whenever the MAF sensor housing size is increased compared to stock, more air will enter the system than the engine management has been calibrated for and you will run leaner. If the MAF sensor housing size is decreased compared to stock, less air will enter and you will run richer.
Fortunately, there are corrections that can be made for changing the size of the MAF sensor housing to allow the engine to run properly which we will discuss later on in this article.
Turbulence
In order to accurately measure the amount of air coming into the system, it is important for the air to flow smoothly across the MAF sensor. Any turbulence in this air flow will create errors in the amount of air measured versus what is actually entering the system.
In the factory air box, the Subaru engineers utilizes a smooth velocity stack style inlet and internal ribbing on the inner sections of the cases to dampen pressure waves and promote a laminar air flow into the MAF sensor housing. The MAF sensor housing itself is straight and smooth internally and positions the sensing portion of the MAF sensor properly in the air flow stream (ie: not offset to any angle left/right or up/down).
For aftermarket intake systems, turbulence across the MAF sensor is an all too common occurrence. Often times the MAF sensor is placed in close proximity to a bend, pipe joint, or weld. In the case of some hot air intakes (ie: Short Ram), the MAF sensor is mounted directly after a conical intake -- well before the air has a chance to smooth out.
When this turbulence occurs, the MAF sensor will suddenly see more or less air then it had previously. This will cause the engine management system to respond by making the engine run leaner or richer for as long as the error from turbulence occurs. The most noticeable driving characteristic associated with this would be a hesitation or flat-spot in the engine's power deliver. A worse case scenario would be the engine suddenly leaning out while under full throttle that resulted in engine damage.
Unlike the errors created by the different size of piping, there are no corrections one can make for an intake design that allows turbulence across the MAF sensor.
Other Considerations
The other issues to consider with upgraded intakes are the filtration capabilities of the element used, the chance for water ingestion or damage from road debris.
Location of the MAF sensor in terms of its distance to the inlet of the turbocharger (or some other point of reference) is not critical so long as the system is free from leaks. Having it too close to the turbocharger inlet can of course create errors from turbulence as can having the plumb-back line from the compressor bypass valve (aka blow-off valve) too close.
Potential Solutions
Now that most of the common problems associated with aftermarket intakes have been outlined, let's discuss what possible solutions there may be for those that run one.
When dealing with the issue of a different MAF sensor housing inner diameter, the best solution we've found is to simply recalibrate the factory engine computer for the new air flow. The factory engine management system has a rather large table of data that basically tells the computer how much air is coming in per sample read. By recalibrating this information, the engine will run correctly -- so long as there isn't also a problem with turbulence.
For those intakes that generate turbulence across the MAF sensor, there unfortunately is no easy solution. Since this turbulence can occur at different points in the power band, based on both engine RPM and engine load, all that can be done to make the engine run safely is to recalibrate the engine with a relatively rich overall tune. While this isn't the best for power, it will help protect the engine.
Conclusion
Overall, the factory air cleaner system doesn't fall into the traditional "first item to replace" like we've all be accustom to. In fact, it may even be suggested that it be one of the last thing you do in your quest for power.
From our testing, we've found the stock air box to work well even at 350-375 HP. From that point, packaging requirements for other necessary modifications such as front mounted intercooler may require the use of an aftermarket intake.
The best solution for an aftermarket intake will be either one that has been designed to use the stock inner diameter for the MAF sensor housing or one that has a tuning program behind it to support the change in MAF sensor housing size. If there is any turbulence in the design, however, this will negate any usefulness of the intake.

 

That K&N must not have been "properly oiled"

 

Don't confuse people with facts

 

I might just keep my cai. If my engine burns up ill slap the factory back on tell them they suck.

 

So you do get power gains. Lots of bolt ons don't give huge gains, or give more significant gains in addition to other things.

I put a CAI on my 2000 V6 Mustang for a few reasons. What I really noticed, however, was the improved mileage. I gained about 7mpg. The old stock system was fed through the fender, but what was different on the new system was the filter and opening was almost 400% bigger (it narrowed once inside the wheel well on the stock system) and there seemed to be better routing for the air tubes. Also, my parts guy personally guaranteed I will get better mileage, so I'll keep track and see if I get my old parts back.

As for K&N, I had put them in several vehicles, but the ones that made the big difference was the Ranger and the Sedona. My Ranger I used to have to downshift seven times on the highway between the town I lived in, and the next one. Switched to a K&N, suddenly I wasn't downshifting once on that run. On the butt dunk, the truth was I find't notice a difference on the straights. The Kia was a 2mpg difference, and for the amount of travelling we did at the time, it was worth it.

Other cars I didn't measure mileage, nor did I have anything to really measure power against.

 

why is this not stickied. there is some wonderful info on here.

i dont dis those that have and swear by. whatever floats your boat. but for those asking the question: "would i benifit from aftermarket intake?" this info is invaluable

 

X2

 

This shouldn't be sticky'd. This entire post is comprised entirely of opinions, not facts. You can find a website or forum remark about CAI's that goes along with one's opinion all day long. However, it is just that, an opinion. It is undisputed that a CAI provides improvements to an engine. Smaller gains can be had with drop in filter media. If one purchases cheaply made media, then they will likely have issues. It is possible to have a well filtering media with high flow. One way to do this is square inch availability to decrease the differential pressure. Regardless, this entire post originated from someone believing an unknown source on the internet and running with it. Personally, I run CAI's on all of my vehicles and have hundreds of thousands of miles with no issues directly related to a CAI.

 

But it says they are bad news in the title...and it was read on a forum post written by some guy....so it must be true!

 

I lot of people are disputing that. Many of the CAI aren't even cold air.

 

I believe that the key problem with CAI filters is that they are very small. What you have is a small surface area with a lot of air blasting past it at high velocity. That means that in order for it to satisfy the volume demands of the engine, it has to be very open and unrestrictive, which is the same as poor filtration. The OEM filters are huge things, lots of surface area, and in great big boxes. This means that the air flow per filter surface area is much lower, the air velocity is much lower, and the filter can be much tighter in order to restrict damaging particles and protect your engine.

I suggest that for the very very minimal power increase that you might get from aftermarket intakes, it really isn't worth it. Even if the engine's longevity isn't important to you, the relative benefit is so small that you can't possibly actually feel it. Most people feel it psychologically, made up from the extra noise that it creates, and the expectation that it will make a huge difference.

 

I agree with worthywads... you can NOT make a claim that Cold Air Intakes provide improvements to an engine without a lot of disclaimers. First off, the stock intake IS a cold air intake so what are you really gaining? some of the so called cold air intake systems actually draw in warmer air than the stock intake would. Secondly, the stock setup will filter air better than a high flow system. So how can you straight faced say that a CAI is an improvement to an engine when it forces the engine to burn dirtier air? The people that really need and will benefit from a high flow system are the ones who's intake is restricting the engine. You might see some minor top end gains from a CAI system, but for most people those gains are either in an RPM range that they never use or it's not worth the trade off in air filtration to get those minor gains.

 

So back to sticky'n it?

 

No worries. I was thinking sticky'n it would cut down on the CAI posts...........

 

Those guys are hacks!

 

Use of the search function would cut down on a lot more CAI posts than applying a sticky to yet another CAI thread

 

I've actually seen dyno numbers go down with the air cleaner removed. One case in particular was a 460 Ford with a downdraft throttle body. Modern engines cannot be improved in any tangible way with modifications to the intake and / or exhaust. A percent or two gained at 5,000 RPM is a percent or two lost at 3,000. The only way those improvements come into play is with increased flow through the head (porting, modified cam profiles, etc). I have never seen a dyno proven exception to this. Marketing and bullshit butt dyno claims are what keep this crap rolling.