K&N filters really improve fuel economy?

prius - no
improve fuel economy - not noticeably.

 

If you change your air filter with a standard, but good quality paper filter regularly, there will be no added improvement in MPG.

From K&N's website:

1.How will a K&N filter affect my vehicle's fuel economy?

There is a relationship between air filter restriction and mileage. The theory behind this is simple, the harder an engine has to work to suck air through the intake tubes and air filter, the more gas gets wasted in the process. Replacing a dirty or clogged air filter is one of many recommendations the U.S. Department of Transportation suggests for improving fuel economy (see http://www.fueleconomy.gov/feg/FEG2007.pdf). Many K&N users report an increase in their fuel economy after beginning to use our air filters, as noted on our testimonial page. However, these experiences do not mean you will also experience a change in your mileage. We certainly understand why it is theoretically possible for a consumer to experience a mileage increase after installing a K&N air filter or intake system, however, we do not go so far as to make a general claim that our air filters and intake systems will provide an increase in mileage.
It is virtually impossible to make sweeping and general claims about mileage. Even the EPA fuel rating numbers for new cars are often not representative of the mileage you actually experience. There are many variables that affect mileage such as: tire inflation, the type of fuel, weather, elevation, the speed at which you drive, the gear in which you drive, the speed with which you accelerate, engine maintenance, excessive idling, cruise control, the grade of motor oil you use, and of course, the condition of your air filter. In short, mileage is complicated.
K&N filters are less restrictive than disposable paper or synthetic air filters and K&N Intake Systems are less restrictive than the factory installed air path. So K&N filter technology could be an important tool, when combined with other elements, to help keep mileage as high as possible.
Oh yeah, there's one more limitation imposed by science. If you take advantage of added power by driving more aggressively, you will reduce mileage. You cannot have your cake and eat it too.

 

They will not improve mileage on a closed loop OBD-II car. All passenger cars sold in the USA since 1996 are OBD-II.

The reason it cannot improve gas mileage is that OBD-II cars sense both the amount of air, post filter, going into the engine and the state of combustion of the exhaust gas. The fuel/air ratio is dynamically adjusted to keep it at what the car thinks best at the moment.

A more restrictive filter will simply lower the air flow, and the car will compensate by either lowering the fuel flow, or slightly opening the throttle butterfly.

The only time a less restrictive filter has an effect is at or near full throttle. In this case a less restrictive filter will let in more air when the throttle butterfly valve is fully open, which will burn more fuel making more full power output. If one races a Prius than a K&N filter might make sense in order to win the races, otherwise it is a waste of money, or worse.

Worse? Yes, worse. UOA have often shown that some oiled K&N filters may let in more dirt than paper filters. This shows as elevated silicon from road dirt. Silicon is highly abrasive to the metal in engines and may increase engine wear and decrease service life. For racing cars which are rebuilt often this doesn't matter. I would prefer never to have to have my Prius's engine rebuilt.

Test evidence that these filters, and that clog filters have no effect on gas mileage:

www.fueleconomy.gov/Feg/pdfs/Air_Filter_Effects_02_26_2009.pdf

Rumple

 

OK OK... I'll toss in my personal experience...

First off, there is no reason to install an oiled filter in the Prius as opposed to the standard paper element types. The paper elements are superior to oiled foam IF THEY ARE REPLACED WHEN THEY SHOULD BE.

If you are a lame mechanic and don't change the air filters when you should, an oiled foam element CAN give you some additional time to get to the thing and change it without doing some damage to the cylinder walls from dust scoring.

Secondly, the K&N filters are one of the most reliable systems for a performance car... however, they cost 5x as much as a standard filter or more; and they still must be recharged (cleaned and reoiled) to remain effective as a filter.

I have had quite a number of performance-based automobiles, some stock (like my avatar) and some quite heavily modified for track, off-road and/or single use (drag strip only)... and I used both the K&N system and paper elements... I will say that an over oiled K&N filter WILL gum up the air sensors in a throttle body and give the wrong readings to the fuel delivery computer and you will suffer on the low end especially. I will also say that in a heavy dust environment, the K&N didn't perform any better than the paper elements did... but in a high humidity environment, the K&N was superior to the paper element filters after 60 days in nearly application I put it on.


My recomendation is to stay with a quality paper air filter element.

 

This has come up in a number of car forums.

Briefly, all the manufacturers are trying really hard to improve gas mileage. If a different filter can improve mileage, everybody would be using it.

As somebody else says, a lower restricted filter is only better at full throttle.

I worked with filter manufacturers and seen the data. Unlike what most people think, a dirty filter actually works better at cleaning the air. That's because the layer of dirt acts as a second filter. Dirt attacts and remove more dirt by mutual attraction and a layer of particles (dirt) can function as a filter. Think of filtering water through sand. The downside is that the filter becomes more restrictive. However, as discussed above, this is only a worry at full throttle. Of course, this is talking about a reasonable amount of dirt.

Now engine oil filters (the ones used for filtering engine oil) may always work at full capacity so this does not apply to dirty engine oil filters. Also, engine oil filters has a bypass when it is too clogged so you don't want the engine to use the bypass.

There is no bypass for an air filter.

Air filters do not work at full capacity because the throttle is not fully open 99% of the time. For air filters, not at full throttle, a little dirt does no harm. And if you happen to use full throttle, your mpg is shot anyway so don't worry about saving mpg at full throttle. As another poster has said, the butterfly provides even more restriction during regular working conditions.

 

The K&N will result in slightly better fuel mileage, due to lower pumping losses of a lower restriction filter. How much? Probably not enough to be measurable. In theory the Prius would be a prime use for a K&N, why? Because the Prius Atkinson cycle engine is optimized to run at low RPM and high throttle openings. At lower RPM there is less frictional losses, and high throttle openings there is less pumping loss. Simply it's more efficient.
So in theory a K&N would result in better fuel mileage, but it may not be that simple as the more sophisticated engines are, the less likely you can make a simple change and things get better.
In theory you would get better mileage if you remove the muffler, but thankfully I haven't seen any Prii with "fart can" exhausts.
You would be best served to keep it stock, and keep it highly maintained. Proper maintenance would probably make more difference than anything else

 

Would using one be a problem if you had to have warranty work done on the ICE? I know GM was saying the K&N filters were resulting in ring's wearing out because of the filters letting more dirt into the motor. Witch kkinda makes since, more likely to happen if you don't oil the filter the right way. I always thought the K&N filters can't help MPG much if at all. and since they do allow more air through i wonder how much dirt and dust they also let through. I have heard stories of guys having trouble getting warranty work done on chevy trucks, GM was saying the after market air filters let to much dirt into the motor letting parts wear out early.

 

The K&N, or running with no air filter at all, will result in no MPG difference in a closed loop OBD-II car. Far larger than any restriction in an air filter is the throttle butterfly valve.

Please read the report in the link I posted above. In it, they covered air filters with shop towels to increase the restriction so much that the air filters were deformed by the pressure differential - there are pictures of these filters. They found no MPG differences at all, even with these absurdly restricted air filters. A K&N it will nothing for you MPG but will lighten your wallet.

If you are racing, or otherwise going for maximum output from a motor, then a K&N or low restriction filter might make sense as in such usage a wide open throttle is used more often and the additional air would make for more peak horsepower.

Rumple

 

This was my concern after I purchased a K&N for my Nissan Frontier PU a few years ago. I noticed that when the filter was held up to the light you could see many little pin-holes straight through the media! I then performed a test where I sprinkled talcum (baby) powder on the filter with black paper underneath. Some of the powder made it through the filter on its own! If this happens without any airflow, imagine what it would be like with a pressure differential pulling through the crud. I've been intending to repeat the experiment after cleaning and oiling the filter, but haven't gotten around to it yet.

 

It wans't that the K&N was affecting the rings. The problem is that the over-oiled K&N filter would send oil through the intake tract and coat the MAF sensor wire and this would cause bad readings. Then the PCM would send confusing signals to the transmission and cause a very bad lag in shifting (slipping) and could lead to transmission failure. I had this happen to me back when I was racing GM cars/trucks (all 2000-2002 models). In my Trans Am it was was so bad that the trans would fail to shift and just bang off the rev limiter which I had set at 6,500 rpm. I cleaned the MAF sensor and cleaned the oil off the K&N and it everything was fine. Many other K&N users reported similar results when they over-oiled the filter.

 

rumpledoll,
The K&N will result in slightly higher fuel mileage, period. It has nothing to do with air to fuel ratio, as you state correctly, that will be automatically compensated for. It has to do with the fact that there is a slight efficiency loss whenever there is a vacuum present in the intake manifold. That is one reason that diesels are more efficient than gas engines and one reason that I believe the Prius engine operates at full throttle more than you think it does. I believe the Prius engine is throttled by RPM and valve timing at least as much as it is by throttle opening. A "normal" engine with a "normal" transmission, this is not as possible as it is in the HSD. Ken at Japan, will I hope correct me if I'm wrong, or hopefully will put light on the subject as my guesses are just that.
K&N's do not filter as efficiently as a paper airfilter will. Real easy to prove this, in a K&N equipped car, remove the K&N and wipe with a tissue paper the intake tract behind the filter. See how dirty it is. Now do the same thing in a paper filter equipped car, see how dirty it is. Compare the two. K&N type filters have sacrificed filtration for less restriction. The argument is "how fine do you need to filter the air". Yes over oiling a K&N will junk up the MAF, especially if you have the fine wire type of MAF, they are easily cleaned if you junk it up so bad it trips a MIL, but the problem is that the MAF may be affected, but not enough to trip a MIL.
Bottom line, we all theorize that Toyota will sacrifice engine life in order to SLIGHTLY increase their CAFE by specing an inferior oil, but don't give them credit enough to install an airfilter that might slightly increase their CAFE?
Trust me if putting an "intake tornado" or "fuel line magnet" on your car made a difference, the factory would have one on it.
I would guess the increase in fuel mileage of a K&N airfilter would be about the same as installing "Baby Moon" hubcaps.
Save your airfilter money and use it to buy a good tire air pressure gauge. You'll save more fuel and money that way I'm sure.

 

With regards to the K&N, I ran a K&N cone-type filter on my Honda for about 10 years & cleaned & re-oiled it regularly. After looking at it during those times I would agree that it filters the air less well than a paper filter, due to larger "openings" (for lack of a better word). It sounded nice but I would not do that for my Prius. So I would be somewhat careful about that. And although I don't think it was related, I've had the transmission replaced and engine replaced in my Honda - I attribute it to hard driving & launching the car for fun & quarter-mile times, but who knows.

 

I've noticed an interesting thing about this Forum. For some reason we just don't want to give Toyota or any manufacturer credit. We seem convinced that there are "magic" speeds that will result in better fuel mileage than slower speeds will and continue to insist that you get better fuel mileage in "power mode" than in ECO mode.
If there were speeds that resulted in greater efficiency, don't you think Toyota would tell us? And if power mode resulted in greater mileage, why would Toyota even have an ECO mode?
For the majority of people, drive the car and maintain it in the manner the manufacturer recommends and you will have the most satisfactory owner experience possible.
For those that want to push the limits and are willing to change their driving habits to maximize efficiency, there are many things that can be done, and I'm sure many Forums that stress that above all else. Clean MPG comes to mind.
But, I assure you, nothing can increase the efficiency of this car more than learning to drive it in an efficient manner, and that is free.

 

I've owned 4 cars in my lifetime. I have used the K&N filter in 3 of them. I didn't get one for the Prius because the other 3 cars have had noticible decrease in fuel economy after installing a K&N filter. Back then, speed was my main interest.

It seems more air going through your engine means more gas and money out of your wallet.

I went though a "Fast and Furious" period some years ago...

 

No and that's why I hoped Ken or someone similar would chime in. I too have the Scan Gauge and do not know what the throttle position is. Is it the position of the gas pedal? Or the throttle plate? Is it even calibrated to anything?
I do know that efficiency wise it's better to operate at low RPM's and high throttle openings, and with the CVT it's possible for Toyota to do that. I assume they do, but don't know.
Point is, anything you can do to lessen the amount of work the engine has to do to fill the combustion chamber with air, the more efficiently it will operate, but how much more so? For instance waxing your car will reduce the air drag which will increase mileage, but almost certainly not enough to be measurable. I put the K&N in that league.
I'm sure you can find literature to support higher mileage claims from K&N, I haven't looked.
K&N's have their place, I use a 12 sq. ft. K&N to filter the air in the Pratt and Whitney turbine powered aircraft we manufacture, but I don't see it as an advantage in the Prius.
Surprised I haven't seen anyone asking about cold air induction, there is of course a theoritical advantage there too.

 

I ran into this Prius throttle control We all know who Hobbit is, this I'm sure is a Gen II car, and I'm sure most of it applies to Gen III. Of particular interest is this paragraph

"But on the way back from Hybridfest, the real epiphany came to me.

It was an observation that lasted only about a quarter-second, but which
completely confirmed all of this new thinking. I was on some secondary
highways in Pennsylvania, and had just come down a fairly large hill that
had run the battery up to its displayed "full" at 80% SOC. In that state,
the hybrid system often tends to get a little confused and try to do things
to bleed off some of the charge -- such as by starting and stopping the
engine a few times, and various other thrashing that is a bit less smooth
than the usual control scenario. After the downhill, I was coming up a
gentle rise toward a red light, and trying to use the injection meter and
vacuum gauge to stay just barely "under load" while still letting my speed
gradually fall. During the next run/stop transition, I suddenly heard a very
brief but aggressive "rev-up" from the engine -- like you would hear upon
stabbing the clutch pedal on a manual transmission while cranking uphill in
high gear. The motors, just for an instant, had evidently "let go" of the
engine's output, and then just as quickly recovered and rebalanced the
torque. But that blip ran the engine RPM up so fast that I realized that
my vacuum gauge had never lied to me -- when it read low, the engine was
indeed running in a high-torque mode, even if I couldn't really feel it
pushing the car. I thought about it a little more, and realized that even
though the engine was running barely above idle -- 1100 RPM or so -- the
throttle was significantly open, shaft torque was high, and RPM was being
kept down by the "heretical mode" electrically-routed overdrive feeding
straight into the road load. *There* was my "high gear" answer. It was
already happening -- I didn't have to do anthing except make sure I kept the
system demand down near the low end of my "sweet spot", but not let it drop
down past there. Toyota's throttle-control strategy took care of the rest.

It's bloody brilliant."

 

I found this on this site,don't know how to properly link it, so I cut and pasted it.

Quote:
Originally Posted by pulse
Does the 2ZR-FXE actually have valvematic?
No.
Instead of that, the 2ZR-FXE has the EGR system to reduce O2 intake air, then it runs wide open throttle for reducing the pumping loss.
The result is 220g/kWh very efficient gasoline engine.

Ken@Japan

 

So,
It would seem that the Prius engine does run at low RPM, but high throttle opening, sort of "lugging" the engine for greater efficiency. But apparently I was wrong about varying the valve timing at low RPM and high throttle opening, it seems that Toyota accomplishes the same thing, but probably better by dumping a whole lot of exhaust gases into the intake. I didn't take emissions into account, they obviously do.
The manner in which the PSD allows the engine to operate at an almost limitless RPM range as well a being able to pull power from the traction battery and the computer having complete control of the engine independant of the gas pedal has allowed operating conditions that are not possible on a conventional car.
This thing is far more than an electrically assisted internal combustion powerplant that has regenerative capability. It may have started out that way, but I theorize that the PSD has opened up entire operating strategies that were just not possible before. Probably would have been an exciting time to be a Toyota Engineer.

 

Yes if your old filter is dirty & clogged! Filter like K & N.are design for high volume air flow , high reving. Short stroke engine , the Prius engine is neither high volume nor high rpm. It's a long stroke engine design to provide power at lower rpms. 2nd the Prius engines are design to run lean, check the exhaust pipe it's clean compare to muscles car exhaust they are blacks with carbon. 3rd. The Prius is design to suck in Hot air with minimum low air flow so the ecu makes adjustment to run lean as possible yielding less gas being burned. Of course that means less power! If you plan on running the Prius around 5-6,000 rpm all the time Yes the K&N. Will meet your needs. My question is why prius?