Debate continues: K&N filter vs. MPG
 

[ EDIT: from MetroMPG - I made a mess splitting this topic into a new thread. I had to "quote" some users' posts below to move their comments over here. But the quotes below are the original words made by the person quoted. ]

I've also noticed that I've gotten a slight but noticeable increase in fuel economy after replacing my OEM Air filter to a K&N Filter.

Was the old filter plugged up dirty? :)

I personally don't buy the K&N = better fuel efficiency idea.

If you look through their web site, you will not find ONE single corporate claim that their filters improve fuel economy over a clean, OEM filter. Why? Because if they did that, they'd have to prove it in court when they are sued by the EPA for misleading advertising. You better believe if they really thought their filters helped MPG, they'd be advertising the heck out of that.

Instead K&N relies on customer testimonials about MPG. Unfortunately, that anectdotal testimony isn't worth the electrons it travels on.

DifferentPointofView quote
 

DifferentPointofView said:

Yeah, I should have been more clear - I wasn't challenging their flow claims. Those aren't hard to believe.

I'ts just the MPG testimonials that make me bristle. One of my big pet peeves is claims made with no sound data to back them up.

But you've also got a point on the warranty. There's something to be said for reusing a K&N filter for the life of a vehicle instead of throwing away another OEM style filter every NNN miles.

thealterecho quote
 

thealterecho said:

The most significant flow restriction in a gasoline engine is the throttle plate, not the air filter. The only time I'd grant that an air filter will aid fuel efficiency is when the engine is operating at WOT, and the effective restriction shifts upstream from the throttle plate to the filter and possibly the intake tract.

But since we don't drive around at WOT, it's a moot point.

I also stick by the marketing argument: if K&N believed their filters boosted fuel efficiency, they would be marketing the crap out of that angle.

But they don't, because the know they can't prove there is any significant difference. So instead, they dance with customer testimonials, knowing full well that the majority of their customers don't have the inclination or ability to empirically determine the filters' effects on fuel efficiency.

I'm gonna have to say that the vehicles that will see the most improvement if there is any would have to be the ones with the larger filters. If you have a lot of air to filter and your using a restrictive air filter, using a less restricting one on a lot of air will see the most results.

It's like someone who just ran 3 miles compared to someone who didn't, and they're both breathing through small straws. The person who just ran 3 miles will need a lot more air than the person just standing and recording time. So if the person who ran 3 miles moves to a much larger straw, they will see much more results than the person who was recording time.

From there website.
I think that we need to keep in mind that the power setting that are used in driving for FE are very low and that large volumes of airflow is not required. I have experimented with aluminum restrictor plates placed just before the butterfly with a 1/2" hole. The top speed was 65 MPH WOT. FE stayed the same on level terrain but during 1/2 mile climb the FE increase due to the throttle setting required. When I increased the opening the FE advantage disappeared and with the original opening the car was really undriveable because of acceleration rates.

One thing about the hunt for FE is that all cars react differently to modifications even between 2 of the same model. It depends on a lot of uncontrollable factors. Even changing the oil when changing the air filter could show in increase in FE just do to the oil change. Tank to tank testing really is not an accurate way to test for a mileage increase. YMMV (Your mileage may very)

I had my doubts about the K&N for my Impala, but after installation of the filter, I have noticed a difference and an overall increase in fuel economy when driving carefully. Now, having said that, my fuel economy is worse as well when I stomp on it. More airflow is perhaps allowing the ECM to work a little more fuel into the mix, at least this is the basic rational I have come up with.

Prior vehicles - 68 Plymouth Fury II - K&N filter allowed better low range takeoff and an overall improvement (no numbers to back this, just seat of the pants and over a year of having it in there)
-- 90 Plymouth Acclaim (3.0L V-6) figure a rough average of 3 mpg improvement depending on driving conditions.
-- 89 Chevy S-10 (2.5L 4 cyl) strangely not much mpg improvement noticed, but a definate improvement in getup and gooooooooo

FWIW, I have seen people cite used oil analysis done on the same engine run with a K&N filter and a disposable paper filter, and the oil that was run when the K&N was in use showed higher amounts of silica. Which isn't hard to believe if you think about it, more airflow = less filtration.

I know I posted this in another thread, but I'll do it again.

Air Filtration Test

My theories on increased mpg with K&N filters are as follows
1) some EFI systems are in someway fooled by the minor change in airflow.
2) the AFM / MAF is slightly damaged (well documented that the oil on them does harm sensors) and causes a lean condition.
3) (My personal favorite!) most people install them as Cold Air intakes, under the warm hood, typically factory intakes draw from a much colder area (fender/ headlight), therefore what they are installing is a Warm Air Intake.
4) Aliens from Mars
5) (second most probable in my book) It's just a placebo effect. And may be furthered by people maintaining their vehicle when they do the install.

It's been well documented that the filter is a very small part of the overall inlet restriction. It's also well documented that if you're driving for fuel efficiency, you will not be needing anywhere near the max airflow.
So to me it seems that any K&N benefit (much like "synthetic" oils) is from a placebo effect.


I would like someone with a scangauge to run tests with the most clogged filter they can find, a clean K&N, and no filter at all. (and don't worry about that last one, I know a guy who ran a 283 Chevy for 100,000 miles with no filter at all)

Any takers?

Hmm, sorry, dont like the idea of absolutely no filter to prevent stuff from being sucked into the intake. As far as a placebo effect goes, and other doubts, there can well be times when a filter upgrade does not work as intended. For my results, I have the improvements based on numbers so I am content with what I see as a positive result.

On the wife's intrepid, we put in a "drop in" k&n and removed the sound reduction box, replacing it with a smooth tube. No other chages were made. 2mpg around town and 3 on the highway additional has been observed for better than 60k miles. I still clean and re-oil the thing every 10K miles and I have a standard paper filter that I put in while it dries overnight. It is consistant that we lose that 2-3mpg whenever the paper filter is in.

Now, this is how it reacts to one car. I have also seen cars where acetone worked, and others where it did not. Some where a certain brand or weight of oil made a difference. I think it may, in part, have to do with the design of the intake and engine of the car.

The neon has one, but that was to get rid of the "habitrail" intake that dodge put on the first generation neons. And yes, I am running it as a warm intake, so I would not just say that the k&n made a difference....but certainly the whole system did (about 3 mpg).

As long as there are different cars and motors out there, and people wanting to achieve different goals with them (speed, power, FE, reliability, whatever)....I think the great K&N debate will continue.

Jim

When I bought my Ranger, it has a K&N in it. It was running rough, and I realized that the MAF sensor was gummed up. I suspect it's the gunk that you use to "oil" the K&N, and after the first time I had to clean it, I realized that it's a messy job, and the old oil and dirt ends up in the storm drains, so I just tossed it and went back to the OEM. Absolutely no difference in mileage or power (though it runs better now that I cleaned the MAF.)

Not to go off subject; but synthetic oil does allow you to increase FE; not because of magic; because you can run a lower viscosity oil, which flows better; saving energy.

I think we can all agree that the SGII will not be capable measuring for this test. THE SGII works off of reported Engine Load which is based on airflow; if the K&N flow was the benefit then the throttle plate would close more, ending up with the same airflow and same reading.

[QUOTE=nascarnation;64856]
(and don't worry about that last one, I know a guy who ran a 283 Chevy for 100,000 miles with no filter at all)
I know 2 people who routinely run without airfilters.

1) Honda civic with Prelude engine swap; picked up a rod knock on second oil change, sand could be seen in the oil and the filter was entirely plugged (bypass stuck, low oil pressure actually caused the rod knock)

2) 2003 Trans Am Full exhaust, cam, tune, built auto, 3500 stall, no air filter. ~40,000 miles to date with no issues; however he does have a fine "pre filter" on the car. . . . ..

science and the K&N
 

I recall a very long and heated debate with respect to the K&N over a year ago at maxmpg.One member posted a laboratory investigation of air filters.As an air filter,K&N lost on all counts,least effective in removing particulates from the passing air stream,and fouling sooner than any other filter tested.------------------------ K&N is a holdover from the day of the oiled horsehair filter,long since abandoned by the auto industry and even lawnmower manufacturers.---------------------------- The solvents and oil required for maintaining the filter over it's service life,help perpetuate N.America's reliance on foreign oil,add to airborne VOCs,and help destroy the US balance of trade.--------------------------- It's my opinion that K&N should be limited to racing applications,where the engine operates in a controlled environment,and has no place in ecomodding.Premature engine failure do to accelerated piston ring wear runs counter to efficiency.

Measure the pressure drop of the whole intake, and measure just the pressure drop of the filter. What you'll find is that your filter is very likely the smallest restriction in your intake. Do it at various rpm and you'll probably find the filter accounts for less than 2 inch of water below 4000 rpm.

The eleminating negative boost articles at autospeed are a good read.

Production of the F-Body cars (Camaros and Firebird/Trans Ams) ended after model year 2002. ;)

poop you are absolutley correct; I'll call him in the morning and see what year his car is. Ls1 car. . .

If you could run a 5W20 syn, there's no reason you couldn't run a 5W20 petro. Viscosity is viscosity I think.
Perhaps a 0W20 syn might be better in cold weather (they don't make 0W20 petros that I'm aware of).

nascarnation: that's my understanding of synthetic oils as well - a small potential benefit to vehicles operated in cold climates (to minimize the warm-up hit). There's a reason the big oil co's don't advertise that synthetics will save fuel... if they could, they would.

I think this the whole point that everyone has made about "worthless unless WOT". If you let off the throttle for the correct speed, you now have the airflow (air blockage) you need to correctly drive the car. Doesn't matter where in the intake it is, that is what you want. At WOT, you hope to have even more airflow than before, hopefully enlarging a BSFC island. If you aren't in a suddenly found new island, you didn't get any benefit.:(

On the other hand, has anybody seen real gains from reducing exaust backpressure? There aren't any hard requirements to reduce airflow after combustion (some pressure helps keep it even), so I would expect any MPG gains to be made here.

This is purely anecdotal, because I don't have good records before/after.
However adding a Dynomax "cat back" to my Jeep 4.0 appears to have hurt the mileage.
Since it is considerably louder, I'm assuming it has less backpressure.
If I had a do-over, I'd go with stock or equivalent muffler.

Lower backpressure than stock seems to hurt low end torque, and good low end torque is good for mileage. Sure the lower backpressure helps for those who like to race, but not for us.

Depends on a lot of factors, though. A friend of mine put headers on his 65 Mustang, and gained some fuel economy. (It went from "unbelievably hideous" to merely "awful". ;) )

Any potential gains are probably a lot smaller for more modern cars, though. I'm guessing much or most of the FE benefit for him was the stock system having a pretty poor design.

-soD

This is going to be long, but the bottom line is that I may have figured out why some folks are seeing better mpg after installing k&n filters.

I'm going to assume that we are dealing with vehicles that have an electronic engine management system. In addition, I'm assuming that the engine management control program's goal is to hold the air/fuel mixture at a constant target value as measured by the O2 sensors. I'm also assuming that the program is written as a closed loop feedback loop with feed forward. A regular feedback control would wait for the O2 sensors to move away from the target O2, then start changing fuel rate to get the O2 back to target. This control is relatively slow. Feed forward is provided by using a mass air flow sensor. The feed forward speeds up control. In fact, if the feed forward were perfect, there would be no reason for feedback.

So, I think it's supposed to work like this. The manufacturers want a certain target level of richness/leanness in the combustion chamber. They use O2 sensors to measure this, and decide on a target O2 level for the control program. You also have a starting air/fuel ratio target. So, you step on the throttle, the throttle plate opens, and the MAFS sees air flow, and uses the ratio target to set the fuel flow. The O2 sensor reading should be on target, but if it's not, it will change the air/fuel ratio setpoint.

Knowing this, as most of y'all have figured out, a high flow filter like the K&N should not change mpgs. There would be better performance at or near full throttle. But otherwise, all you're doing is taking less pressure drop across the filter, which is being compensated by more pressure drop across the throttle plate.

One of the Chevrolet truck forums is full of claims of improving mpgs by adding a K&N filter, and also, by cleaning the MAFS. Neither one of these SHOULD affect mpgs at STEADY STATE. But while driving, everything is constantly changing. It's possible that the control program just doesn't work as well when a K&N filter is installed, and that the engine may run lean, on average. In the same manner, a dirty MAFS may cause the proram to run rich, on average.

What do y'all think?

I fully believe, from experience with my Ranger, that the K&N is the cause of the dirty MAF. Mine started causing problems within 10,000 miles of the cleaning and re-oiling of my K&N, and after a cleaning, had similar problems about 10,000 miles later. I think the MAF gets contaminated with oil from the K&N.

I replaced my K&N with a stock filter 40,000 miles ago, and had no further problem with my MAF since.

A dirty MAF sensor would cause a lean condition if anything, since more air is entering the engine than the computer is seeing.

Yup, with engine-damaging pinging.

The filter may make more HP,because to measure HP,you have large throttle openings, and airflow becomes important.If the stock filter flows 500cfm and the K&N flows 550,then the motor will make more power.
(assuming it can use the extra CFM.)

For MPG and daily driving, you have small throttle openings and the throttle reduces airflow.

It is likely that the stock filter( which is sized for Wide open throttle) will flow more than enough air without restriction at small throttle upenings. The extra air flow of the k&N is not needed or realized by the engine.

If the engine only needs 100 CFM,it does not matter that the K&N flows 550CFM, it already has more than it needs.

I use a round cone type filter, but it's a stainless steel mesh, like 4 layers thick. I haven't really tested it for airflow or anything, but it sits in the same location as the stock filter did on my Civic, and with the 3" mandrel bent "cold air intake" (eBay special) it seems to be working fine. Oil changes haven't shown any evidence of crap in the engine, and I drive on farm roads with it alot.

The car is sold, but I'm keeping the filter, I'll probably put it on my wife's Grand Prix for now. It's a serviceable filter, that apparently will last "nearly forever". You clean it with warm soapy water, just like your dishes, and there is no oiling necessary. APC makes it. (I know, I know... )

I've personally never seen a gain from K&N filters, and don't plan to speculate on why or why not. I don't care to pay the kind of money that they cost, and then maintaining the filter beyond that, and the vehicle maintenance issues that they're apparently known to cause. I'd rather use a "normal" serviceable filter, like the stainless mesh I have now. IF I ever feel that it's not performing on a particulate filtering level, I'll just add a washable pre-filter to it. (ShopVac FTW!)

To hush the speculative claims that increased airflow through the filter causes better fuel mileage in typical scenarios:

This one is simple, and I can't believe that no one has thought to do it.

If you think your OEM filter is restrictive in normal situations, I want you to set your engine at a specific RPM with the throttle, and have someone watch the tach, or hook up an external tach that you can watch.

Loosen the clamp that holds the air pipe to the filter box, and remove the air pipe from the filter box so that the engine is now "breathing freely". If you notice a change in engine RPM at this point, your OEM filter is creating restriction in your normal driving situations. If no discernible changes are noted in RPM, your air filter is NOT creating restriction in your intake tract.

Another way to test this is to go buy a K&N intake "drop-in" filter. Measure the vacuum at the pre-filter opening in the intake tract, both at idle and at 20% throttle with 0 load using your OEM filter. Use the same procedure to test vacuum at the pre-filter intake opening with the K&N filter installed. The figures at both idle and 20/0 should be either exactly or nearly exactly the same (no more than .5 inHg variance) for both tests.

If they're not, the OEM filter is restrictive during normal driving situations, and the K&N filter may provide some flow benefit for you.

i got mileage gains when i switched from my air intake to a cone and when i changed my exhaust. i went from about 9 mpg to 15 city on average.

But, if the engine control system DOES work as I described, an MAFS that is reading incorrectly shouldn't affect how rich or lean the mixture is. At steady state, the feedback from the O2 sensors should compensate by generating a new fuel/air inlet target, which will, in turn, get everything back to normal.

As far as the test proposed in the previous post, I don't think it will prove anything if the electronic engine control DOES work as I suggested. If you increase the air flow, the MAFS will see it. Since the feedforward control maintains a air/fuel target, the fuel flow will be increased. It will run faster.

Assuming the same engine control system, here's something interesting that should happen. Say you're driving down the road at a steady 60 mph. Your goal is to maintain that 60 mph. Now, let's say I have a genie remove the air filter completely as you're driving. The MAFS sees a higher air flow. The engine control system sees the higher flow, and since it's trying to control the air/fuel ratio at its current target, it increases the fuel flow. (No, you haven't pressed the gas pedal down any more.) As a result of the inrease of air and fuel, your vehicle speeds up. Since your goal is to maintain 60 mph, you lift your foot off the gas pedal a little (which closes the throttle butterfly a little). Air flow decreases, which causes the fuel to decrease. Eventually, you're back at 60 mph, using the same amount of air, and same amount of fuel. The only difference is that you are at a lower throttle position. In other words, the restriction in the air flow has just moved from the air filter to the throttle plate.

haha love the sig man

I'm sorry, I think I have to tell you that your nick is accurate at this point.

Under vacuum, higher flow doesn't occur until the engine requires it to. Period.

It doesn't matter if you change the filter, or just remove it altogeher. There is no more flow at 50% throttle with a K&N than there would be at 50% throttle with a paper filter, or no filter at all. That's just how it works.

The largest restriction in an air throttled engine is, and always has been, the throttle plate. As long as whatever blockage is before the throttle plate has less restriction than the throttle plate itself for a given throttle setting, there is no more or less airflow than the engine would have under the same throttle setting with a completely open intake tract.

a 6 mpg gain for an air filter and new exhaust?

hmmm



my ranger lost mileage when i switched from a stock airbox to a cone K&N (complete setup)

The '94 Pathfinder is rated for 14 mpg city, so maybe a plugged cat or muffler was causing the 9 mpg. My Ranger didn't get any better mileage with the K&N, and actually got worse mileage once the K&N contaminated the MAF. (The fact that the pinging eventually blew the electrode off of a spark plug probably didn't help either.)

There is no debate. Only the gullible who think a drop in air filter will cure cancer.

That synthetic K&N oil is majick, lemme tell ya. It's like Windex!