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DifferentPointofView 12-05-2007 10:30 PM

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.

MetroMPG 12-16-2007 01:40 PM

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.

MetroMPG 12-16-2007 01:45 PM

DifferentPointofView quote
DifferentPointofView said:


Actually, A magazine did a test on after market filters, from brands like AEM, K&N, and other name brands I can't think of. As far as filtration goes K&N Finished on top of the filtration part, and I know that on their boxes it provides an Air Flow Comparison Chart in CFM on Average Disposable Aftermarket paper Air Filter vs. an oiled Cotton Gauze K&N filter in both typical Round and Panel Type Filters. Also, If you go onto you can view a complete test protocol with results on a particular vehicle and what was observed.

A typical round filter was tested, and filtered out 548 CFM, and a K&N did 881 CFM. A Panel Did 319 CFM while the K&N Panel Did 441 CFM.

Now I This is just filtration data, As for MPG I dont know, but some tests would have to be had to get accurate data.

I really didn't buy a K&N filter for the MPG part, It was more for the 10 Year 1,000,000 mile warranty and how I didn't have to keep buying new filters all the time, Minimizing landfill. And All I have to do is use their cleaner to get out the gunk, and rinse it out, then re-oil. I like the landfill Idea most probably. And I save money cause the re-oiling stuff costs less than a new OEM ZJ Filter. And It will hopefully outlast the car itself.

MetroMPG 12-16-2007 01:46 PM


Originally Posted by DifferentPointofView
Now I This is just filtration data, As for MPG I dont know, but some tests would have to be had to get accurate data.

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.

MetroMPG 12-16-2007 01:47 PM

thealterecho quote
thealterecho said:


Originally Posted by thealterecho
Think about this. The stock filter creates a resistance when the engine is sucking in air,some vehicles more then others.Think about when you put 2 cups together that are nearly the same size. When you go to pull them apart it is almost inpossible at times because there is a resistance. This is example is to give you a good idea although it is not exactly the same because one side of the filter is not completely blocked off to air as the cup. But if you poked a small hole in the back of the cup then the cup that was slid in would come out easier. If you make a big hole on back of the cup it will come right out. Because the air did not resist. It flowed straight thrue the cup that had a cup in it. Same concept. Resistance abosrbs energy.

Not only does it create less resistance but it makes for a more combustible enviroment enabling the engine to compact more air into the cylinder at any given time.

It is only logical that a better flowing filter make better MPG.But that does not mean it flows signifigantly better on every vehicle it is apllied to so I am not saying all vehicles will see an increase but I have never had a vehicle not increase in MPG or power with a K&n filter. I cant speak for anyone else.

MetroMPG 12-16-2007 01:47 PM


It is only logical that a better flowing filter make better MPG.
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.

DifferentPointofView 12-16-2007 01:57 PM

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.

Lazarus 12-16-2007 10:15 PM

From there website.

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.
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)

Unforgiven 10-01-2008 10:01 PM

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

Formula413 10-01-2008 10:45 PM

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.

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