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#1
Old 04-17-2013, 08:30 PM
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Any Proof That K&N Airfilters DO Anything?

K&N air filters are claimed (by the mfg.) to have all kinds of amazing benefits-higher gas mileage, more power, etc. Yet, no auto mfg. offers them as OEM equipment. Why is this? If they provide no benefit, isn't K&N indulging in fraud?
Has anyone ever scientifically tested these things? what were the results?
#2
Old 04-17-2013, 08:34 PM
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I think it's safe to assume that car manufacturers don't use them because they're expensive and require maintenance that virtually no (regular) car owner is going to do. I had one once, I really don't want to go back to hosing off my air filter and re-oiling it when, instead, I can just get a new one when I get my oil changed for a fraction of the price.

As for the claims to increased HP, I'll let someone else answer that.

Also, there's plenty of things that can increase HP and give you more power, but aren't included as stock equipment, that doesn't mean the claims aren't true.
#3
Old 04-17-2013, 08:46 PM
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Aside from those filters that are used on the "Cold Air" kits, the only advantage of the OEM replacement filters is the ability to clean and re-use them. Over time, and depending how often one is inclined to change air filters, this could be a cost saving.
#4
Old 04-17-2013, 09:20 PM
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IIRC, many years ago I read a Consumer Reports study comparing air filters, and K&N was among the best. But that was a long time ago, and my memory is a little fuzzy.
#5
Old 04-17-2013, 09:55 PM
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Can someone explain how K&N's claims work? How could you get both more power and better fuel economy by using a (supposedly) freer flowing air filter?

Isn't the air-fuel mixture very precisely controlled in a modern engine? I can see how more air could mean more power, but only because it would allow you to burn more fuel with it. But how does that help fuel economy?
#6
Old 04-17-2013, 10:00 PM
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As a general rule, modern fuel injection systems don't leave a whole lot on the table in terms of power and especially fuel economy. Replacing a single component, like an air filter, isn't going to have much of affect, because the OEM has already made sure that the air filter is not a bottleneck in the system. As you say, if it were worth .5 mpg, the OEM would already be doing it.

Now, if you replace the entire intake tract and the intake manifold and the exhaust header(s) and the exhaust system, then re-tune the computer to deal with all that extra airflow, you can usually (but not always) make some power. Fuel economy is trickier, since there's almost no inefficiency in the combustion chamber anymore.

Back in the day, when fuel economy wasn't as important and computers weren't as sophisticated, there may have been some truth to K&N's claims, especially on big domestic motors where the specific output (horsepower/displacement) wasn't particularly great. And then, measuring horsepower is an inexact science. Two "identical cars" can come up with different numbers on the same day and the same dyno, then add on top of that different environmental conditions and different dynos and you can get a shift knob to show a 20hp improvement.

K&N's can still be good if you want a reusable filter and have the energy to oil it periodically -- the oil makes it better at catching particulates than a non-oiled filter. But as to claims of hp and mpg, I think those days are done.

Last edited by steronz; 04-17-2013 at 10:01 PM.
#7
Old 04-17-2013, 10:14 PM
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I've known several engineers in the auto manufacturing business. They get daily pressure on designing, manufacturing and incorporating parts that can meet standards but might only save $.010 per part over what is currently being used. To the number-crunchers it adds up.

A K&N air filter doesn't even get close to the radar screen. Buyers want sound systems, premium interiors, back seat media centers, wheels that stand out and other flashy add-ons. An air filter, forget it. Anybody that cares about it will do it on their own. Also, anybody that cares about their air filter will know when they buy the car that the dealer is charging them double or triple for something that they can install in 10 minutes by themselves.
#8
Old 04-17-2013, 11:49 PM
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Originally Posted by Furious_Marmot View Post
How could you get both more power and better fuel economy by using a (supposedly) freer flowing air filter?
It takes energy to pump air through a filter. If the resistance to airflow is less, the energy required is less, which can mean more power and/or better fuel economy.
#9
Old 04-17-2013, 11:58 PM
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Originally Posted by Joey P View Post
I think it's safe to assume that car manufacturers don't use them because they're expensive and require maintenance that virtually no (regular) car owner is going to do. I had one once, I really don't want to go back to hosing off my air filter and re-oiling it when, instead, I can just get a new one when I get my oil changed for a fraction of the price.
And, to sort of expound on this, one major difference is that when paper filters fail they stop flowing and cause running issues that will alert the driver and/or trigger a check engine light, but no permanent engine damage is done. When the owner neglects the service on an oilable filter like a K&N, the filter quits filtering but still flows fine and there's no indication there's a problem and they start letting gunk into the engine. Paper filters are a lot more forgiving and considering the very minimal at best performance difference, it's a no-brainer for the OEM.
#10
Old 04-18-2013, 09:52 AM
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Originally Posted by Joey P View Post
I had one once, I really don't want to go back to hosing off my air filter and re-oiling it when, instead, I can just get a new one when I get my oil changed for a fraction of the price.
I definitely understand not wanting to deal with the gauze filter, but the "fraction of the price" thing I'm not sure on. Paper filters aren't nearly as cheap as they sound...I recently bought one for my wife's Jeep Grand Cherokee, and it was over $20. At the same auto parts store, the drop-in K&N filter for that vehicle is $49.99. So, three paper filters and you're right at the cost of the K&N plus the cleaning kit that will let you can clean and re-oil it a bunch of times.

I have one on my M3, but I don't bother on the Jeep...that 4.0L engine is not going to be fast no matter what kind of air filter it has.
#11
Old 04-18-2013, 09:58 AM
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Originally Posted by ralph124c View Post
K&N air filters are claimed (by the mfg.) to have all kinds of amazing benefits-higher gas mileage, more power, etc. Yet, no auto mfg. offers them as OEM equipment. Why is this?
Because cars are not designed to be as good as they possibly can be. They're designed to be as good as they can within specified manufacturing and cost limitations.

Traction control makes cars accelerate faster and corner better, with no downside beyond cost. Nonetheless, it's not standard on all vehicles. Alloy wheels are lighter and stiffer than steel wheels, which reduces unsprung weight and provides marginal benefits in all sorts of areas. Again, no downside other than cost, but not standard on all vehicles.
#12
Old 04-18-2013, 10:41 AM
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K&N air filters suck balls. You can hold them up to the light and literally see through them. I don't mean that they're translucent, like a paper filter might be, but that they literally have pinholes that you can see light through.

You're essentially trading off effective filtration for freer flow if you use one of these.

And like others have said, if the air filter was a economy or emissions bottleneck, they'd have cured that in one way or another already- that kind of thing is LOW hanging fruit when compared to stuff like stratified charge or direct injection.
#13
Old 04-18-2013, 11:21 AM
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Quote:
Originally Posted by SpeedwayRyan
... the "fraction of the price" thing I'm not sure on. Paper filters aren't nearly as cheap as they sound...I recently bought one for my wife's Jeep Grand Cherokee, and it was over $20. At the same auto parts store, the drop-in K&N filter for that vehicle is $49.99. So, three paper filters and you're right at the cost of the K&N plus the cleaning kit that will let you can clean and re-oil it a bunch of times.
It's a game of pennies to the automakers. The way for them to make a million dollars is to shave one dollar of the cost of a car and sell one million cars. If Filter A costs $20 and Filter B costs $50, there's no way they'll use Filter B unless there's a government mandate to do so.

An even more extreme example of this is the olives in airline salads. It's claimed that American Airlines saved as much as half a million dollars per year by removing one olive from each first class salad in 1987. A more conservative calculation pegs the savings at about $50,000 per year, but the point is seemingly microscopic changes can yield significant financial results.
#14
Old 04-18-2013, 11:33 AM
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Originally Posted by SpeedwayRyan View Post
I definitely understand not wanting to deal with the gauze filter, but the "fraction of the price" thing I'm not sure on. Paper filters aren't nearly as cheap as they sound...I recently bought one for my wife's Jeep Grand Cherokee, and it was over $20. At the same auto parts store, the drop-in K&N filter for that vehicle is $49.99.
Ummm....If a paper filter is $20 and a K&N filter is $50 how is that not a fraction of the price. I mean, if you want to nitpick, if one is $45 and the other is $46, it's still a fraction of the price, but in your own example, we're talking less then 1/2.


Of course, I'm surprised at how expensive paper filters have become. About a year ago I needed to get my oil changed. When they asked me if I wanted the air filter changed, I asked how much it was and it was something like $30. I told them just to leave it in, assuming I could pick up a new one for $10 or so. Nope, made a few calls while I was waiting and all the auto stores where selling them for about the same price.
#15
Old 04-18-2013, 11:46 AM
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Originally Posted by steronz View Post
As a general rule, modern fuel injection systems don't leave a whole lot on the table in terms of power and especially fuel economy.
This. Several years ago a bunch of BMW motorcycle enthusiasts decided to test the claims. They dyno tested several bikes with factory air filters, K&N filters, and NO filter, and made several runs.

There was exactly zero measurable power increase.

The claims tend to work like this:

-Factory air filter produces 1.5" H2O pressure drop.
-Wonder filter produces only 0.5" H2O pressure drop.

Wonder filter is 300% better!!!

This ignores the fact that atmospheric pressure is about 384"H2O. Therefore a 1.5" pressure drop represents, at most, a 0.3% power loss. If the improvement were directly proportional to pressure, then the wonder filter might produce a 0.2% power increase, which is completely buried in the noise of temperature variations and barometric pressure changes. But this is not the case. Mass flow varies as the square root of pressure drop, so that difference in pressure allows only 0.1% more mass flow.

The actual difference is even less than that though. Because the filter is only part of the total pressure drop between open atmosphere and the inside of the cylinders. Most of the drop is still going to be getting past the intake valve(s). Tuned intakes can mitigate this over narrow rpm ranges, and this is of course where peak torque is measured, so really sensitive measurements may pick up an improvement in peak torque, but anywere else the pressure loss across the filter is meaningless.

As for fuel economy, you might conceivably reduce pumping losses AT FULL THROTTLE. Otherwise, a less restrictive filter just allows you to close the throttle a bit, creating exactly the same conditions in the intake manifold.

This assumes a modern fuel injected engine. Carburetors are far more sensitive to filter restriction, and a restrictive filter can cause rich running and poor fuel economy.

While carbs have vanished from cars for decades now, they were still being put on street bikes as recently as a few years ago (maybe still, I have not kept up) and they are common in off-highway motorsport vehicles, lawn tools, etc.

Last edited by Kevbo; 04-18-2013 at 11:47 AM.
#16
Old 04-18-2013, 12:30 PM
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Paper elements provide better filtration, period. THAT is why OEMs still use them. The only reason to use cloth is that it is reusable by cleaning and re-oiling.

Last edited by Kazo; 04-18-2013 at 12:31 PM.
#17
Old 04-18-2013, 12:46 PM
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Originally Posted by Joey P View Post
Ummm....If a paper filter is $20 and a K&N filter is $50 how is that not a fraction of the price. I mean, if you want to nitpick, if one is $45 and the other is $46, it's still a fraction of the price, but in your own example, we're talking less then 1/2.


Of course, I'm surprised at how expensive paper filters have become. About a year ago I needed to get my oil changed. When they asked me if I wanted the air filter changed, I asked how much it was and it was something like $30. I told them just to leave it in, assuming I could pick up a new one for $10 or so. Nope, made a few calls while I was waiting and all the auto stores where selling them for about the same price.
You reuse the K&N so your $50 is spread over the life of the vehicle (or at least several years), whereas you're buying a new $20 paper filter once or twice a year.
#18
Old 04-18-2013, 01:38 PM
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Originally Posted by SmellMyWort View Post
You reuse the K&N so your $50 is spread over the life of the vehicle (or at least several years), whereas you're buying a new $20 paper filter once or twice a year.
Once or twice a year? Not on a modern car. Engine air filters typically have a 30,000 mile replacement interval, once every two or three years for most drivers.
#19
Old 04-18-2013, 02:09 PM
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Originally Posted by Kazo View Post
Paper elements provide better filtration, period. THAT is why OEMs still use them. The only reason to use cloth is that it is reusable by cleaning and re-oiling.
This is essentially it (bolded part). If you search the web you can read all day long, and probably tomorrow too, on car related message boards, about the K & N vs paper debate.

I have one in my Trans Am but most of the guys on the car nut web site I frequent have gone back to paper.

As far as being able to see through the filter, here is an explanation off a truck site from a K & N representative, so take it for what it is worth.

http://thedieselstop.com/content...20The%20Editor

The potential problem with these filters is that many people over-oil them after cleaning. This often deposits oil on the wires of your MAF (mass air flow) sensor and leads to problems and/or sensor failure.

When you first take the new filter out of the box it has a nice, uniform orange color. So people spray the shit out or their newly re-cleaned filter to make it look the same.

The problem is that the new filter is only lightly oiled before packaging at the manufacturer and the oil migrates throughout the filter over time while it is still in the box. More time than you are going to take when you clean it. Thus the over-oiling issue and your engine will suck that over-sprayed oil across your MAF sensor.

I clean mine about 3 times a year and get a certain amount of satisfaction from seeing all the crap that gets washed out during the cleaning process.

The cleaning process is also something that many people will not have patience for. The dirty filter gets sprayed with cleaning soap, let sit for a bit and rinse it under the faucet. Then wait while the cotton filter batting dries out naturally, no hair dryer. Then lightly re-oil. Might take all day. If you are a car guy that is no problem, for the average user probably too long.
#20
Old 04-18-2013, 02:30 PM
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Originally Posted by Joey P View Post
Ummm....If a paper filter is $20 and a K&N filter is $50 how is that not a fraction of the price. I mean, if you want to nitpick, if one is $45 and the other is $46, it's still a fraction of the price, but in your own example, we're talking less then 1/2.


Of course, I'm surprised at how expensive paper filters have become. About a year ago I needed to get my oil changed. When they asked me if I wanted the air filter changed, I asked how much it was and it was something like $30. I told them just to leave it in, assuming I could pick up a new one for $10 or so. Nope, made a few calls while I was waiting and all the auto stores where selling them for about the same price.
Right, it is, but you only buy a K&N once. Wasn't trying to argue your exact words, just the idea that paper is cheaper in the long run. It doesn't take very many filter changes for a K&N to pay for itself. Total lifetime cost, paper filters don't end up as a fraction of the K&N, which has a million mile warranty.

If paper filters were a few bucks, there would definitely be an advantage financially...but they are 20 or 30 bucks every time you change them and a K&N is 50 bucks and 10 bucks for a cleaning/oiling kit, and the whole package will last the lifetime of your vehicle.

That said, paper filters are easy and safe and like I said, I use them on my wife's car.

Last edited by SpeedwayRyan; 04-18-2013 at 02:32 PM.
#21
Old 04-18-2013, 02:44 PM
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Sounds like BS to me... "In fact, those pin holes are what makes a K&N filter efficient. Within those holes, there are actually hundreds of microscopic fibers spanning them"

I have to think that if that was the case, we'd have a bunch of nearly transparent pre-oiled cotton disposable filters being used by OEMs. Instead, we uniformly get opaque or translucent dry paper filters, or possibly pre-oiled paper filters from both the manufacturers AND the vast majority of aftermarket makers like FRAM, Purolator, Mann, etc... Only K&N pushes this oiled gauze stuff, and basically claims that they know something that huge companies like Honeywell (parent of FRAM) don't.

It just doesn't stand up to my sniff test.

Last edited by bump; 04-18-2013 at 02:44 PM.
#22
Old 04-18-2013, 02:52 PM
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Originally Posted by SpeedwayRyan View Post
I definitely understand not wanting to deal with the gauze filter, but the "fraction of the price" thing I'm not sure on. Paper filters aren't nearly as cheap as they sound...I recently bought one for my wife's Jeep Grand Cherokee, and it was over $20. At the same auto parts store, the drop-in K&N filter for that vehicle is $49.99. So, three paper filters and you're right at the cost of the K&N plus the cleaning kit that will let you can clean and re-oil it a bunch of times.

I have one on my M3, but I don't bother on the Jeep...that 4.0L engine is not going to be fast no matter what kind of air filter it has.
I went to rockauto.com and looked up air filters for a 2005 Jeep Grand Cherokee with a 3.7L V6 engine. The cheapest is $3.39 and the most expensive is $13.40.

They have the best prices and the best service of any online auto parts business I have ever used. They are the amazon of auto parts.

On topic, factor in the cost of K&N's cleaning and re-oiling kit when deciding between them or paper.
#23
Old 04-18-2013, 03:09 PM
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Originally Posted by toofs View Post
I went to rockauto.com and looked up air filters for a 2005 Jeep Grand Cherokee with a 3.7L V6 engine. The cheapest is $3.39 and the most expensive is $13.40.

They have the best prices and the best service of any online auto parts business I have ever used. They are the amazon of auto parts.

On topic, factor in the cost of K&N's cleaning and re-oiling kit when deciding between them or paper.
I have been factoring in the cleaning kit -- but you're 100% correct, RockAuto is insanely cheap. We have a 2004 GC with the 4.0 inline six, but even those are really cheap on that site. At the local auto parts store, they are an easy $20. On RA, even the good name-brand filters like Wix and Mahle are in the $10-15 range.
#24
Old 04-18-2013, 03:22 PM
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Originally Posted by bump View Post

I have to think that if that was the case, we'd have a bunch of nearly transparent pre-oiled cotton disposable filters being used by OEMs. Instead, we uniformly get opaque or translucent dry paper filters, or possibly pre-oiled paper filters from both the manufacturers AND the vast majority of aftermarket makers like FRAM, Purolator, Mann, etc... Only K&N pushes this oiled gauze stuff, and basically claims that they know something that huge companies like Honeywell (parent of FRAM) don't.

It just doesn't stand up to my sniff test.
I'm not a K&N zealot by any means, although I do have one on my project/weekend toy car. Same car also has modified exhaust, cams and remapped fuel injection.

The two parts of you statement that I disagree with are

(a) the idea that manufacturers would use oiled filter technology if it was actually better. As has been stated numerous times in this thread, manufacturers consistently make decisions with an eye on the bottom line. Just because a manufacturer uses a certain type or brand, does not mean its actually better. The most obvious example of this is tires. Unless you are $50k or more for your car, you can almost bet the tires on it are lowest bid items, not the best tires available for your car. Manufacturers also know that the average person who treats their car like an appliance isn't going to maintain an oiled filter.

And (b) you will never win any argument about filtration by using FRAM as your chosen champion. Pretty widely noted by car enthusiasts as the lowest quality filtration product you can buy.
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#25
Old 04-18-2013, 04:48 PM
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Originally Posted by leftfield6 View Post
And (b) you will never win any argument about filtration by using FRAM as your chosen champion. Pretty widely noted by car enthusiasts as the lowest quality filtration product you can buy.
Only for oil filters; their air filters are pretty highly regarded.
#26
Old 04-18-2013, 05:57 PM
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When I used to follow a used oil analysis / motor oil forum, there was a definite trend towards higher silicon levels in the oil of vehicles that used them.
That is to say, people who used K&N had more contamination from sand/etc making it past the filter.
The contamination wasn't at dangerous levels, but it almost always be an extra 5-10 PPM.
#27
Old 04-19-2013, 11:43 AM
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Originally Posted by R. P. McMurphy View Post
I've known several engineers in the auto manufacturing business. They get daily pressure on designing, manufacturing and incorporating parts that can meet standards but might only save $.010 per part over what is currently being used. To the number-crunchers it adds up.
I worked for Ford around 1980. The rule of thumb used to be:

Spend $1M overhead cost to save $0.25 variable cost, on a common engine part.

No doubt the ratio has changed since they sell fewer cars and more expensive ones, but there's definitely still a strong motivation to save every penny they can on variable cost.

That rule was hard on the guys doing the engine processor coding, because not only did the cheaper sensors & actuators usually require more complex code, the guy making the decision looked better on his end while spending money in a different department. The result was always needing to stuff 5 lbs of code in a 10 lb bag. I was glad I wasn't one of those guys!
#28
Old 04-19-2013, 11:51 AM
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Originally Posted by gotpasswords View Post
It's a game of pennies to the automakers. The way for them to make a million dollars is to shave one dollar of the cost of a car and sell one million cars. If Filter A costs $20 and Filter B costs $50, there's no way they'll use Filter B unless there's a government mandate to do so.

.

But there is. Govt mandated fuel economy numbers are a bear to meet. If GM could add an extra .5MPG for $30, they do that whaaaaaay before throwing 10 times that for a lesser gain.
#29
Old 04-19-2013, 06:27 PM
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Originally Posted by DrDeth
But there is. Govt mandated fuel economy numbers are a bear to meet. If GM could add an extra .5MPG for $30, they do that whaaaaaay before throwing 10 times that for a lesser gain.
After they've done all of the free or nearly free things like taking 40 pounds of spare tire and jack out of the trunk and replacing it with a can of fix-a-flat, and removing two pounds worth of rear floor mats, and so on... If they thought they could fill tires with hydrogen to make them weigh an ounce or two less without exploding, I'm sure they'd try it.
#30
Old 04-21-2013, 12:20 PM
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There'll only ever be niche markets for K&N filters as it's so much easier to fit a paper filter. Domestic car OEMs will never fit them either - even if they weren't more expensive - as the hassle of cleaning, drying and re-oiling isn't a positive selling point.

That said, I've been using K&Ns for years and I think they're great. I generally clean them every 2000 to 3000 miles, as it only costs a few pennies and an overnight wait for the thing to dry out. My current car has 206,000 miles on the clock (135,000 of which were with K&N filtration), and there's no sign of filter oil deposits inside the airbox. That K&N filter has paid for itself many times over.

I find it very noticeable when the air filter is getting clogged (paper or cotton) as the engine's power curve starts to get lumpy, making the gear changes less fluid and making the car lurch a bit when the throttle is lifted. As an observation, it seems that the filter performance is impaired if it looks grubby to the eye.

I have briefly run (non-ECU) cars with the air filter removed*, and there's a distinct power boost. I reckon I get a couple of extra horses from a K&N filter compared to a stock paper type. It's not a huge boost, but it does follow that a freer airflow is going to produce more power.

* I don't recommend this. Top Fuel dragster engines don't have air filters, but then they're stripped down and rebuilt every half a mile.
#31
Old 04-21-2013, 12:46 PM
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I use a K&N because it looks better on my exposed-edge air cleaner assembly.
#32
Old 04-21-2013, 02:17 PM
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Amsoil filters do not require oiling for filtration but allow for better airflow.

I use one on my cold air intake. Combine this with a retune of the ECU to "teach" the computer to do with all the extra air it's getting, and my butt dyno feels a definite increase in power.
#33
Old 04-21-2013, 04:15 PM
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I'd like to see actual dyno tests AND oil analyses showing that the HP/torque goes up, and that the internal engine wear doesn't increase, before I'd consider a K&N.

Last I saw, HP/torque increased marginally, but the wear was noticeably higher (as measured by Si, Fe and other compounds in used motor oil).
#34
Old 04-21-2013, 04:18 PM
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Originally Posted by bump View Post
I'd like to see ... oil analyses showing ... the internal engine wear doesn't increase, before I'd consider a K&N.
You're never going to see that. K&N results in higher silicon, which will result in higher iron/aluminum/etc readings.
There might be one wonky analysis that shows it, but I've seen a half dozen analyses that all showed K&N results in higher wear numbers and none that refuted it.
#35
Old 04-22-2013, 09:00 AM
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Originally Posted by Kevbo View Post
As for fuel economy, you might conceivably reduce pumping losses AT FULL THROTTLE. Otherwise, a less restrictive filter just allows you to close the throttle a bit, creating exactly the same conditions in the intake manifold.
To elaborate on this with a specific hypothetical example:

-to cruise at 75 MPH, a car needs 40 horsepower from its engine. In stock condition, this requires the throttle plate to be opened to a particular position.

-We replace the stock air filter with a K&N filter that has less flow restriction. Now when we open the throttle plate to that same position, we get 40.1 horsepower from the engine.

-40.1 horsepower means we are cruising faster than we were with the stock engine. So we back off the accelerator pedal a smidge, and the throttle closes just a smidge, until the engine is making 40 horsepower just like it was in its stock configuration. In both cases, the total intake tract restriction, i.e. the sum of the throttle plate restriction and the air filter restriction, is identical, resulting in identical airflow and identical power output - and therefore identical fuel economies.

The ECU is of course paying attention to throttle position, but as long as the engine is operating in closed-loop mode, it's watching the exhaust O2 sensor and adjusting the fuel injection rate so as to maintain ideal air/fuel ratio even when the throttle position is a fraction of a percent off of what it would have been in a fully stock engine configuration.
#36
Old 04-22-2013, 09:31 AM
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Quote:
Originally Posted by Mr. Slant View Post
You're never going to see that. K&N results in higher silicon, which will result in higher iron/aluminum/etc readings.
There might be one wonky analysis that shows it, but I've seen a half dozen analyses that all showed K&N results in higher wear numbers and none that refuted it.
Exactly. Higher silicon and wear metals means that the K&N filters don't filter as effectively as the standard paper filters.

I suppose it all comes down to whether or not one's willing to trade off a slight increase in power for a measurable difference in internal engine wear due to ingested sand and other particles not stopped by the filter.

Makes sense for autocross or some sort of track car, but for a daily driver, it seems kind of dumb, if you ask me.
#37
Old 04-22-2013, 09:42 AM
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Here is the best test of air filters I've seen so far. They followed ISO filtration testing standards, so their data may actually mean something.

Of the nine filters they tested, here's the highlights:

-the K&N had the worst filtration.
-the K&N had the second worst dirt capacity (before reaching the flow restriction limit).
-the K&N passed the second most dirt.
-the K&N had the lowest initial flow restriction (as noted upthread, the difference is tiny even at WOT, and irrelevant at any part-load condition, plus it clogs up more quickly than other filters, restricting air flow).

Check out the plots there for the details. Very informative.
#38
Old 04-22-2013, 09:59 AM
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Quote:
Originally Posted by bump View Post
Makes sense for autocross or some sort of track car, but for a daily driver, it seems kind of dumb, if you ask me.
OTOH, I've changed a lot of paper filters that had accumulated no more than a teaspoon of crud in 10-15,000 miles. This may be a case where the hard numbers don't really matter and a moderate amount of filtration is for all practical purposes as good as "perfect" filtration.

I'd have to see studies where some small amount of hard particulates contributed significantly to an engine's wear over its lifespan. I suspect that the damage caused by the small amount of extra grit from a K&N disappears into the noise floor.

Vehicles driven in very dusty, gritty, sandy or offroad conditions would be different, of course, but I suspect the wear issues would be proportional and "mostly" filtration would contribute as much protection as tight filtration.
#39
Old 04-23-2013, 02:02 PM
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Remember the glass sediment bowls on farm tractors? Then you had the oil bath between that glass & the intake to the carb.

Paper filters are very restrictive so they are way big to give good flow.

It is all about money........

Best insurance IMO is frequent oil changes. Sure, the oil has not broken down but it is DIRTY. People are just lazy and want it the easy way, not the best way.

No opinion on K&N vs paper.

YMMV he he he
#40
Old 04-23-2013, 02:30 PM
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Quote:
Originally Posted by Amateur Barbarian View Post
OTOH, I've changed a lot of paper filters that had accumulated no more than a teaspoon of crud in 10-15,000 miles. This may be a case where the hard numbers don't really matter and a moderate amount of filtration is for all practical purposes as good as "perfect" filtration.

I'd have to see studies where some small amount of hard particulates contributed significantly to an engine's wear over its lifespan. I suspect that the damage caused by the small amount of extra grit from a K&N disappears into the noise floor.

Vehicles driven in very dusty, gritty, sandy or offroad conditions would be different, of course, but I suspect the wear issues would be proportional and "mostly" filtration would contribute as much protection as tight filtration.
From what I've been able to divine, the real determinant of internal engine wear due to contaminants isn't so much the amount, as it's the size of the particles.

For example, particles below a certain size (5 microns)just flow through the bearings in the oil without actually contacting anything, but larger ones actually catch and grind and cause wear, so long as they're actually small enough to fit into the bearings in the first place (about 25 microns).

Of course, the idea is that if the air filter doesn't get them, the oil filter eventually will, but that doesn't mean that all will always be caught before they can cause damage.


http://theoildoctor.com/client_i...INEFILTERS.pdf
#41
Old 04-23-2013, 02:58 PM
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Quote:
Originally Posted by bump View Post
Of course, the idea is that if the air filter doesn't get them, the oil filter eventually will, but that doesn't mean that all will always be caught before they can cause damage.
I'd question how much airborne (intake) particulates end up in the oil. Air filters prevent particulates from being aspirated and passing through the cylinder. Oil filters remove particulates caused mostly by engine wear and oil clumping. I don't see how cylinder-gas particulates (of a size to cause any wear) could get past the rings or valve guides in any but a very worn engine.

Last edited by Amateur Barbarian; 04-23-2013 at 02:58 PM.
#42
Old 04-23-2013, 03:32 PM
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K&Ns worked much like the old oil bath filters. The pore size was huge but still small enough that the particulate would touch the cotton gauze and stick to the oil. Ever get some K&N filter oil on your hands? If I recall correctly, it was sticky as all getout.

Back in the day (late 1980s) K&N filter pods worked better than the typical airbox for a Japanese inline four motorcycle. The manufacturers were beginning to claim that the newer air intakes were tuned to the bikes and that aftermarket intakes and rejetting would still result in a loss of power. I'm not familiar with today's bikes, but I assume that there isn't that much of an improvement.

Now, if you want to see a dramatic increase in performance, drill a few 1/2" holes in the upstream side of the airbox for a YSR50 or a Yamaha moped. Either would gain around 5-10MPH!
#43
Old 04-23-2013, 04:40 PM
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Quote:
Originally Posted by Amateur Barbarian View Post
I'd question how much airborne (intake) particulates end up in the oil. Air filters prevent particulates from being aspirated and passing through the cylinder. Oil filters remove particulates caused mostly by engine wear and oil clumping. I don't see how cylinder-gas particulates (of a size to cause any wear) could get past the rings or valve guides in any but a very worn engine.
We are talking about 5 to 15 micron particles here; that's in the same ballpark as red blood cells and something like 1/4 the width of a human hair.
#44
Old 04-23-2013, 08:57 PM
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Quote:
Originally Posted by Amateur Barbarian View Post
I use a K&N because it looks better on my exposed-edge air cleaner assembly.
No kidding! And the sound from the intake on my RZ is hair-raisiing!

Last edited by Gatopescado; 04-23-2013 at 08:59 PM. Reason: Decided to leave it. Looks cool. ;)
#45
Old 04-23-2013, 11:08 PM
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Quote:
Originally Posted by Amateur Barbarian View Post
I use a K&N because it looks better on my exposed-edge air cleaner assembly.
And you get a cool sticker for your car.
#46
Old 04-23-2013, 11:39 PM
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Quote:
Originally Posted by sisu View Post
And you get a cool sticker for your car.
That's where they get you. The filter actually costs 99.
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