"Performance" air filter hype
 

This addresses replacement, panel style filter elements (and NOT full "intake kits," such as INJEN):

http://www.bobistheoilguy.com/airfilter/airtest1.htm

Pretty long article. Will read it at leisure. What does it say though? Can somebody post the verdict please.

The differences in pressure drop is next to nil. That means the difference in power and fuel economy is next to nil.

"So what do these results mean? For one, there is very little pressure drop across any air filter, and the difference between the best (K&N) and worst (paper) is very small."

And the "performance filters" let more dirt through and into the engine.:eek:

That's a great article, harddrivin.

Cliff's Notes for joganjani:

Paper/fiber provide better filtration.
Gauze/cotton provides better airflow than either foam or paper.

Therefore: Decide whether you value filtration or airflow more.

It's important to note that colder air DOES make more power.

So will a well designed "ram air" system (which yields slightly higher pressure @ the intake manifold).

Those things weren't within the scope of that article.

A well designed, "ram air" system can yield some (albeit minor) gains in performance and fuel economy.

You can have both! Higher filtration and lower pressure loss by doing something very simple. I could easilly give be better filtration than all these filters and do it with lower pressure loss than all of them too. So Mr. Smarty Pants Harddrivin', do you want to tell me what that simple thing is?????

Prove to me you aren't just a database of facts and figures.

^ two words.

surface

area

More Myth's cut n pasted by 1LE...

Here's the straight dope from K&N about which particulates kill a motor and why a paper filter isn't superior.

"A Word About Filtration Requirements

There are few areas more confusing than identifying dirt retention requirements when it comes to air filters. Most vehicle owner’s manuals remain silent on the point. In fact, few air filter manufacturers publish any information as to the filtration efficiency of their filters. This stands in marked contrast to oil and fuel filters where there is a relatively large amount of information regarding filtration requirements and capabilities. Studies have shown most engine wear is caused by particles 10 to 20 microns in size. K&N air filters, like most quality disposable air filters, provide excellent filtration of these particles.

To ensure our air filters provide a high level of dirt protection, we regularly test our air filter designs using the testing procedure described above. Those tests demonstrate K&N air filters generally achieve overall filtration efficiency in the range of 97% - 98%, while some of our air filter designs have achieved levels as high as 99%. The fact that our air filters at times reach overall filtration efficiencies as high as 99% while maintaining high airflow is a testament to the quality and capabilities of our oil impregnated cotton air filter medium.

On occasion we see “new” air filter media’s developed and sold under the premise they provide increased levels of dirt filtration. More often than not, as opposed to quoting specific efficiency numbers, this “increased protection” is described as increased dirt retention capacity, meaning the filter can hold more dirt before requiring replacement. Remember, K&N air filters have always provided a service life in excess of disposable filters and then only require cleaning and oiling for re-use.

We encourage customers to do their homework and be aware of the filtration capabilities of an air filter before they buy. Our own testing has revealed wide differences in filtering capabilities. We were surprised to see some disposable paper air filters with an overall filtration efficiency as low as 93%. We hope we have provided enough information to ensure consumers know what they are getting when they buy a K&N air filter.

Filtration 101 - A Deeper Cut

Most people believe that all air filters function on a go/no go basis where dirt particles that are larger than the openings in the filter media are trapped while particles that are smaller than the openings can pass right through. A dry paper air filter does function in this manner. That’s why paper filters are so restrictive to air flow. The openings in this type of filter have to be very small to filter efficiently.

The oiled cotton media used in the K&N air filter functions in an entirely different manner. There are scientific principles that determine how an air filter removes dirt particles from the air stream. The first of these principles is known as interception, which applies to dirt particles traveling with the air stream. Air flow will always take the shortest path and as the air is forced to flow around the filter’s fibers some of the particles will contact the sides of the fibers and be captured. These particles are then held in place by the oil or tacking agent in the fiber.

Another principle is known as impaction, which mostly affects larger or heavier dirt particles. Impaction occurs when the inertia or momentum of the particle causes it to deviate from the flow path. In other words the heavy particles do not follow the air stream around the filter’s fibers but instead they run straight into the fibers and are captured.

The most important principle for our use is diffusion, which deals with the laws of physics that govern the motion of very small dirt particles. Small particles are highly affected by the forces in the air stream. Forces such as velocity changes, pressure changes, turbulence caused by other particles and interaction with the air molecules cause these very small particles to become random and chaotic. As a result, these particles do not follow the air stream and their erratic motion causes them to collide with the filter’s fibers. This phenomenon enables an air filter to capture dirt particles that are much smaller than the openings in the media. In addition, the way that dirt collects or loads on the K&N filter is very different. A paper filter exhibits "surface loading" which means dust collects only on the surface of the media. In contrast, K&N filters exhibit "depth loading". The multiple layers of cotton fibers provide many levels of dust retention. This characteristic allows the K&N filter to hold significantly more dirt per square inch of media than the average paper filter. Utilizing these scientific principles, K&N has been able to design an air filter that is very free flowing while also being highly efficient at removing dirt from the air.

Independent Laboratory Test Results

In order to verify our filters maintain filtration levels necessary to protect your engine, we test our filtering media through independent laboratories. The testing procedure used is the SAE J726 air filter test procedure established by the Society of Automotive Engineers (These are the folks who are supposed to know everything)."

The FACT is, a properly oiled cotton filter is just as good or better at removing particulates hostile to an engine as a high quality paper filter...and cotton filters offer superior air flow and service life.

I'm not siding with anyone and I have NO opinion on the air filtration issue, but you have to be really naive to believe that a manufacturer is going to give you an unbiased view on the issue!

It's not about what they SAY, it what they DO. SAE J726 testing procedures aren't determined by them but by the SAE and the results of those tests are the results which were obtained NOT BY K&N but by an independent auditor/testing firm using those procedures.

And here is an interesting take on the myth of ram air positive pressures (or the lack thereof). The fluid mechanics theory behind why ram air at slow speeds can't exist.

"The Ram Air Myth by Dave Rodabaugh

The Ram Air Myth is the most mythical of them all. It differs from the other myths, in that the other myths are misinterpretations of physical phenomena, whereas ram air simply does not exist.

MYTH: Use of a scoop on the front of the vehicle to collect intake air, or provide “ram air” can raise engine performance.

TRUTH: At automobile velocities, there is no ram air effect.

SIMPLE EXPLANATION

The "Truth" statement says it all. How much simpler can it be? The Ram Air effect is a total myth because it simply does not exist. “But Pontiac uses it on the Trans Am, and they know more than you do.” To those who offer this, tsk tsk. Careful reading of Pontiac’s statements on the matter reveal that the HP increase of the WS6 package are a result of a less restrictive intake, and a freer-flowing exhaust, NOT any ram air effect.

So why does Pontiac use Ram Air? Easy! To make people buy their cars! And they are quite effective with this strategy.

DEEPER EXPLANATION

Of all of the applied sciences, fluid mechanics is among the most difficult for many people to comprehend. It is a relatively youthful applied science as well, meaning that it has not had two or three centuries of work to mature into an applied science on par, with say, chemical combustion. To make matters worse, it is mathematically defined almost entirely by experimentally-determined mathematics.

This last point is the true differentiator between those who only understand concepts, and those who can quantify what they are discussing. Truly, quantification is the real skill of the engineer. It is one thing to speak about qualitative issues (the “what” of the physical sciences); it is entirely another to quantify them (the “how much” and “to what extent” of the same). In grade school, students are first taught about “closed form mathematics” and then that these mathematics are typical of scientific expression. A good example of this is Newton’s famed “law of action and reaction”, the mathematical expression of which is a succinct F=MA. So straightforward. So simple. Three variables in perfectly-defined harmony. Given any two of them, the third is easy to nail down.

Unfortunately, a vast, vast majority of the mathematics used in engineering are NOT closed form. Instead, they are multi-variable correlations valid only for a narrow set of circumstances. Deviate from those narrow circumstances, and a new expression must be experimentally derived. Fluid mechanics is almost entirely defined by these experimentally-determined expressions, further muddying an applied science not well understood.

And if there ever were an applied science for which common sense is wholly inappropriate, it is fluid mechanics. Virtually nothing obeys the “common sense” rules of observation, explaining why those who believe in ram air have extreme difficulty in believing that is simply does not exist.

The Deeper Explanation begins with a basic explanation of engine principles. Air and fuel must be combusted at a specific ratio, namely, 14.7 parts air to 1 part fuel (this is a chemical ratio). Stuffing more fuel into the cylinders without increasing the amount of air they also swallow will get no gain whatsoever. So the hot rodder’s adage “more air = more power” is proven correct. Figure out a way to stuff more air into the cylinder at any given RPM and throttle setting, and you can burn more fuel. Since burning fuel is what makes power, more air truly does create more power.

The amount of air which is inducted into a cylinder is a function of the air’s density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’s density. (Denisty is mass divided by volume. Since cylinders are a fixed volume, increasing the density will also increase the mass of the air in the cylinder.) There are two ways to increase the pressure and density of the air inducted into the cylinders:

- Decrease the pressure drop from the throttle plate to the cylinders

- Increase the starting pressure at the throttle plate.

Ram air is an attempt to do the second. Under normal circumstances, the air at the throttle plate is at atmospheric pressure, and this pressure drops until the air reaches the cylinders. Ram air would start the process at some pressure higher than atmospheric, and even though the drop is the same, the cylinder pressure is higher because of the increase at the start.

Just how would this increase in pressure at the throttle plate occur? The oft-wrong “common sense” says, “If a scoop is placed in the airstream flowing around the vehicle, the velocity of the air ‘rams’ the air into the scoop, thus increasing the pressure.”

Why is this incorrect? There are two types of pressure: static and dynamic. Placing of one’s hand in front of a fan, or out of a moving car’s window, clearly exerts a force on the hand as the air diverts its path to flow around it. Most people would say “See? This is a clear indication that ram air works. Clearly there is pressure from the velocity of the air.” Well, this is correct, but only to a point. This is an example of dynamic pressure, or the force any moving fluid exerts upon obstacles in its path as the gas is diverted around the obstacle.

What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.

The point of ram air would be to increase the static pressure, which would correspond to an increase in the in-cylinder air density, and of course, more air. Superchargers and turbochargers do what the mythical ram air purports to do. A supercharger trades the power of the belt and uses it to compress the air in the intake tract. This energy trade-off results in an increase in intake air pressure, more air in the cylinders, more fuel burned, and more power. A turbocharger trades the power of the hot gases and uses it to compress the air in the intake. The overall effect is the same – an increase in intake static pressure.

For ram air to work, it would have to trade the energy of the air’s velocity (as the vehicle moves through the air) for an increase in static pressure (since static pressure is a part of a gas’s internal energy, we see this is TRULY a trade in kinetic energy for an increase in internal energy). Now for the true reasons why ram air is a myth:

- The way for air velocity to be traded for an increase in static pressure is to actually SLOW IT DOWN in a nozzle of some sort. This is easily the MOST counterintuitive part of fluid mechanics for most people. The “common sense” mind says “In order to increase the pressure of the intake, the velocity of the air needs to be increased, just as increasing the speed of a fan exerts more force upon the hand.” Not only does this confuse dynamic with static pressure, but is also misses the point, which is to trade the kinetic energy of the gas for an increase in internal energy. How can this trade occur if the kinetic energy of the gas is increased? It cannot, and in fact, the only way to trade it is to use the velocity of the gas to compress itself – by slowing it down.

- Below about Mach 0.5 (or about half the speed of sound), air is considered “incompressible”. That is, even if the correct nozzle is selected, and the air is slowed down (the official term is “stagnated”) there will be zero trade. No kinetic energy will be traded in as work capable of compressing the air. The reasons for this are not discussed here; the reader may consult any reputable fluid mechanics textbook for confirmation of this fact. In plain English, a car is just too slow for ram air to work.

Still not enough evidence? Here is a little test. For ram air to work, the nozzle must be of a specific shape. The “Holley Scoop” for the Fiero is the wrong shape, by the way. The fact that it has no net shape at all immediately means it cannot effect any kind of energy trade off, so it cannot possibly create ram air. This is also true for the hood scoops on the Pontiac Firebird WS6 package as well, by the way.

What shape must it be? There are two kinds of nozzles. Pick one:

- Converging. This nozzle gets smaller as the air flows through it. It has a smaller exit than entrance. If the nozzle were a cone, the fat end is where the air would enter, and the narrow end is where it would exit.

- Diverging. This nozzle is opposite the other; it gets bigger as the air flows through it. With a larger exit than entrance, the narrow end of the cone is where the air would enter, and the fat end is where it would exit.

So, which is it?

Without hesitation, most of the “common sense” crowd will answer “Converging.” BZZZZT! Thank you for playing anyway! We have some lovely parting gifts for you! Bill, tell ‘em what they’ve won….

The answer is “divergent”. Yes, the nozzle would have to shaped so that the skinny end is pointed into the air stream, and the fat end connects to the throttle plate. How can this be right? Remember, to increase the static pressure of the intake air (which is the true “ram air” effect), the kinetic energy of the air must be traded to compress the air. This is done by slowing the air down, or stagnating it, and the only way to do this is with a diverging nozzle. Ah, but since air is incompressible at automobile speeds, it doesn’t matter any way.

Conclusion

Ram air is a myth because it does not exist, for the following reasons:

- Air is incompressible at any automobile speed., meaning that the kinetic energy of the air cannot be used to compress the air and raise the static pressure.

- The “ram air” nozzles commonly employed on automobiles tend to be the wrong shape. A divergent nozzle is required for ram air. Straight-profile scoops cannot provide a ram air effect.

Select one of the two types of intakes, warm air, or cold air. Beyond that its just about looks."

Flanagan,

You were supposed to let Harddrivin respond!!!!

But you are correct, sir.

You would have been waiting a long time as 1LE doesn't understand these concepts himself, just what he reads by others (who are more often wrong than right).

Actually, I'm buying the guys test. There is not a significant pressure loss difference between the KN and the CLEAN paper filter.

The principle of surface loading with a paper filter is very much a reality. What happens is two things:

The pressure loss increases as the layer of dirt builds and the fitlering efficiency increases as the layer of dirt builds.

So you must deduce two things... A dirty KN flows much more air than a dirty paper filter and a dirty paper filter becomes much more efficient than the KN will ever be. The test Harddrivin site was only done for 500 miles and was performed with clean fillters.

ASHRAE has established guidelines for air conditioning filter performance and the testing to establish said performance. They previously used a percentage efficiency rating which measured the amount of a certain size particle and larger that were captured by the filter. Filter loading is very much an established fact but their new testing guidlines now also measure the ability of a filter to hold dust. This new rating system is known as the MERV rating system.

The following link is a tech bulletin for an AC filter I rep. You can note two things: a graph that shows the percentage of particulate at certain micron sizes on the first page and the static pressure loss of a clean and dirty filter on the second page. The reason the static goes up is due to filter loading. KN quotes a filter efficiency but does anyone know what micron size this relates to??????

http://www.camfilfarr.com/files/prod...a-Flo%20PH.pdf

The lab doing the K&N independant verification uses the A4 "coarse dust" standard which is nominal 0-180 micron size. The MERV standard is more about filter "life" as a measure of performance rather than it's filtering abilities.

Clean or dirty, an oil charged cotton filter is as good as or better than a high quality paper filter at filtering particulates harmful to internal combustion engines. And the difference just becomes even more apparant as paper filters have an extremely limited time of being "efficient".

You're better off running a cotton filter unless you like changing paper filters every 500 miles.

Not always true.

Any given engine can only inhale so many cfms of air.

Any properly selected OEM paper filter is fully capable of handling that task.

Ther "straight dope"...by the people making money on the filters.:rolleyes:

You'll have to phrase the question using proper grammar first.

And don't tell me "by increasing the surface area."

Define "superior air flow."

No stock OEM filter can flow without resistance what the motor can.

Oh, no. Here we go.

The amount of power (vacuum) needed to generate a particular CFM through the filter.

Last time I checked, the SAE doesn't make filters. I'll believe independant SAE standardized testing over some guy using "shade" of filth to determine filter ability. No measurement of particulates in the filter, no standards of testing...variables EVERYWHERE.

No thanks, I'll take the SAE standards over the looks dirty test.

But the quantifiable differences are only ~ 1/10th of a psi.

Says who? Them, after only 500miles under varied test conditions? Check it again at 5,000 or 10,000. Hardly a substantiated claim.

"The darker deposits indicate poorer filtration, and lighter ones better filtration."


Wow, now the SAE should have make their testing procedures as easy as this.

What nonsense from a bunch of benchtop racers. Their test doesn't show ANYTHING other than the wrong way to conduct experiments.

The changing environment is enough to change the results of these tests, which is why the SAE insists on highly controlled conditions and measurable particulate sizes. You're talking 500 miles a filter times how many filters? If you drive all the time the environment changes significantly.

The guy claims to be an engineering student. I have an M.S. in Mechanical engineering and a B.S. in Mathematics and this joke experiment doesn't confirm to ANY standards. They act as if simply using the same car is enough of a control. How amateur.

My profs would have thrown this "study" in the bottom of their birdcages as the methods are sloppy and the conclusions wholly unsupportable.

What people need to see is that the experiment is fatally flawed.

What particulate sizes? Who knows. They just dark versus light to measure filtration quality. Everyone knows that it's particulate size that matters.

What environmental conditions? Who knows, same roads don't mean crap. Air quality changes on a daily basis.

What density of pollution in the outside air? Who knows. Again, these jokes have ZERO control over the environment of their "experiment".

Show me any REAL "independent test" (like the one below) that shows any SIGNIFICANT difference in rear wheel HP between aftermarket "performance filters" and OEM paper ones.

Many LS1 owners swear by paper FRAM filters and have dyno runs to prove it.

http://www.hotrod.com/techarticles/70738/index.html

All of that is true....@ ~ 60 MPH....

It's not true @ 100 MPH.

If it were then there would be no high pressure regions on a car traveling @ 100 MPH...

Define significant difference? From a filter alone 1-3HP is a significant difference. You want a test? Here ya go.

Here's a guy who is a TL owner, unlike you, who actually took their TL to a dyno shop and had it dynoed.

The results were 4RWHP increase from the K&N drop in filter.

http://www.acura-tl.com/forums/showt...highlight=dyno

ACTUAL 2004 TL results showing the improvement of a drop in K&N

http://www.apnastation.com/nitrotiger/ygp251E.jpg

Those results are WELL within the margin of the accuracy of the dyno.

I've seen people run THE SAME configuration on THE SAME dyno and get results that vary by more than that.

Oh, man. Benchtop racing as its finest. Obviously you've never had fluids. There is a difference between static and dynamic pressure. There is a difference between compressing air and moving it. There is no compression of air at 100MPH :rolleyes:

So there are no high pressure zones on a car traveling @ 100 MPH....:rolleyes:

Says the guy who quoted:

-PIAA on superior fog light optics and mounting

-Daniel Stern (who sells only Halogen bulbs) on the superiority of halogen bulbs

Don't bother responding HD, you're going back on ignore right after I post this. I saw your little rolly eyes remark in skeedatl's response and I just had to laugh and get in a friendly little jab.

Mike

I think we should lock the two of you in a room and settle this once and for all.

Where? Hot Rod TV?

I disagree. MERV takes into account efficiency and dust holding capability. Efficiency is the ability of the filter to trap a certain size of particle, typically .5 to 1 micron. If SAE is 0-180 microns and KN is 99 percent efficient, that is pretty bad.