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?
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.
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.
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.
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?
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.
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.
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.
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.
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. 
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.