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What a good air filter can do for your gas mileage...

BrandonM7

Well-Known Member
Nov 23, 2007
1,156
2
For the record, K&N doesn't make a "good" air filter. They make a relatively free-flowing air filter. They really don't filter very well at all.
 
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SilverUberXeno

SilverUberXeno

El Tigre Blanco
Jul 26, 2005
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Eesh. I feel like I work for K&N...

"Our testing has demonstrated that on average, K&N replacement air filters and air intake systems have a cumulative or Full Life filtration efficiency of between 96 and 99%. Different filters test at different efficiencies due to changes in their shape, surface area and relationship to the direction of air flow through the factory air box or test housing. Like most air filters available in the USA, our filters will provide all the engine protection you need.
For more information on our testing, see our K&N Product Testing page."

K&N Frequently Asked Questions (FAQ)

Also see FAQ #23 for an explanation on "good air filter," Brandon.
 

BrandonM7

Well-Known Member
Nov 23, 2007
1,156
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Eesh. I feel like I work for K&N...

You kind of sound like it, too. Surely the people who stand to make money from convincing you wouldn't present the truth in a rosy manner, would they? How about people who don't stand to make money from selling them?

ISO 5011 Duramax Air Filter Test Report
Air Filtration Test

For what it's worth, I have K&N filters in both of my bikes. I consider the airflow more important than the filtering - basically I want all the performance I can get, and K&N filters flow like crazy. Since they pull out more junk than not having a filter, it's a trade-off I'm willing to make. At the same time I recognize that there's a reason that there's a red dirt coating inside my airboxes on the south side of the filter, and that's because K&N filters don't clean the air all that well.

I do like #21 and #23 from the link you provided, though - especially the part where they say in the ISO 5011 test that 11% of the media is under 5.5 microns. 11 whole percent - what about the other 89%? Fact is, 60% of engine wear is caused by particles under 25 microns, and K&N filters don't really go out of their way to remove stuff that small.

Basically a K&N will keep birds and leaves out of your engine. I'm cool with that - I've run plenty of things with no air filter at all. But I'd never buy one to save gas. I buy them for performance. They do an exceptional job of letting an engine breathe (while clean, that is,) and they do an acceptable job of filtering.

But hey, don't listen to me - I'm just a guy with pistons on his workbench. You should definitely take the word of the people that are trying to sell you something. That's what I do, and that's why I have THE HAMMER in my golf bag and hit 425yd drives.
 
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SilverUberXeno

SilverUberXeno

El Tigre Blanco
Jul 26, 2005
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If you're an expert Brandon your words are welcome. I was actually hoping you'd post some conflicting tests. I will read them thoroughly.

Curious though; before I continue- the damage to an engine is caused by particles that enter through the air filter? K&N states that their level of filtration is satisfactory, which is arbitrary since there is no STANDARD. What do you think is a safe level?

Also; with new detergent oils that are in use now, is it necessary to have a restrictive airflow to save for higher filtration? I don't have pistons on my workbench, and though I find the combustion engine VERY interesting, I do not know it like a neighbor. Are the particles taken in through an allegedly poor filter (K&N) picked up in the oil? Or are these two systems in the engine completely cut off from one another?

There are now detergent gases too, right? Shell, I think...

I appreciate your expertise. Keep it coming.
 
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SilverUberXeno

SilverUberXeno

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Wowza. That independent testing is invaluable. I will study the tables more thoroughly.

The question then, I suppose, is what is a safe level of filtration? The K&N coarse testing is 96% versus 99%, but how much does that 3% really affect an engine? The fine dust testing is significantly different, though.

Brandon, based on what you know, what filter would you recommend for the proper balance between airflow and filtration?
 

Wi-Golfer

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Jul 25, 2007
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Are the particles taken in through an allegedly poor filter (K&N) picked up in the oil? Or are these two systems in the engine completely cut off from one another?


The particulate matter ends up abrading the valves, pistons, cylinder walls, etc. The small amount of oil on the cylinder walls actually traps the particles & allows them to do the damage. Basically by allowing this matter into your motor it's pretty similar to using a sandblaster.

And he is correct about K&N filters actually allowing a lot of crap to get thru. It's a tradeoff, how much more throttle response, gas mileage you want, vs how much engine damage you are willing to accept. BTW, these particles wont destroy a motor overnight, it takes a long time but believe me it will happen. Of course if you live in an urban area where there isn't juch dirt or dust you may get 200,000 miles while someone living on a dusty dirt road might be lucky to survive a month.
 

BrandonM7

Well-Known Member
Nov 23, 2007
1,156
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...Brandon, based on what you know, what filter would you recommend for the proper balance between airflow and filtration?

Brother, wouldn't it be great if that question were as easy to answer as it is to ask? I wish there weren't so many variables in play so I could give you an easy answer, but you know that's not the case. If there were an easy answer this wouldn't be such a highly debated topic. Obviously it varies greatly from case to case. My truck (2005 V6 Tacoma) shows less than 1% change in power on a dyno from bone stock to completely disconnecting the intake plumbing. Easy answer in that case - use the most filtering filter you can get, because that's obviously not the bottleneck anyway. Then look to a '90-93 Honda Accord - those cars see an incredible 11% gain on the dyno from disconnecting the intake plumbing. That's huge - it's time to start doing some thinking in that case.

But then of course you have to take into account the cost of repairing the engine, assuming you intend to have it long enough for that to matter. Speaking of repairing it probably sounds ridiculous when we're talking about 95-99% filter effeciency, but that number is really twisted to make it sound like it's not a big deal - but think about it from the opposite direction. If the stock filter pulls out 99.75% of the shit that tries to come through it (made up numbers, btw, just to make the point) and some other high flow filter grabs 95% -- that means the high flow filter is allowing 20 times the amount of junk into the engine that the original one does. Sounds much worse when it's worded that way, huh? But as the K&N site and yourself have brought up, that's only one source of contaminant in the systems of the engine. It is, however, the largest source by a considerable margin - the air/fuel ratio is around 14.7:1, so there's a crapload more air coming in than gas. The oil that's there is there, so it has a huge advantage in filtration - gas and air get one pass through a filter, oil is running through the filter over and over and over -- plus it's a closed system so the only junk added to it are from the air and fuel, taking you back to the 14.7 times as much air as gas thing.

And then of course you have to consider environment - you could live in the PNW with the silt in the air that isn't all that hard, or Utah with the red-rock sands which are a quite a bit harder, or in Mexico where the sands might as well be diamonds.

Your engine could have tolerances so loose that audible piston slap doesn't have an effect on longevity or so tight that using the wrong weight oil will damage the rings.

You really need empircal evidence for that particular vehicle that gives an idea of how important all that shit is in the grand scheme of things. Thankfully, we have this new-fangled intarwebular device at our fingertips these days. More than likely you can find some vague numbers of how much effeciency can be gained, and how prone that particular engine is to failure - obviously that last spec won't be concrete, but it can give an idea of the tolerances and durability of the unit as a whole.

If a filter magically gains you 20% fuel economy in this day of $4/gal gas, and the engine has a proven track record of durability, and it's relatively cheap to rebuild - no brainer, throw that filter on there and ride it out. If it gets you 2% better fuel economy, the engine is known to have problems out that patootie, and it costs $10k to rebuild -- baby that sucker with OEM parts and pray often. Anywhere in between, do the math and decide what makes sense.

If your vehicle is a Kawasaki, a K&N allows the intake to howl so awesomely at full throttle that everything above this line is pointless, hence my motorcycles having them.
 
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SilverUberXeno

SilverUberXeno

El Tigre Blanco
Jul 26, 2005
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I will have to have a chat with my mechanic. I'm not sure he can read but he's a nice fella who has always given me great advice about cars. He has the skills he needs!

"intarwebular". Haha.
 

bugman53

Well-Known Member
Aug 1, 2008
17
0
I have a few things to add. First i own a motorcycle shop and i build race engines for a living. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:eek:ffice:eek:ffice" /><o:p></o:p>
<o:p></o:p>
The first thing is you cannot add ONLY air(oxygen) and get power gains. Oxygen does not burn! It just lets the fuel burn and makes power. In an internal combustion engine there is an ideal fuel to air ratio. It is ~14/1 than means 14 parts air to 1 part fuel that is a perfect fuel burn. If there is more air and less fuel (lean) all the fuel burns with oxygen left over. if there is more fuel and less air then there is a rich mixture and all the fuel does not burn and it is spent out the tail pipe. so you cannot just pump more oxygen into a motor and get more power without increasing the fuel. I will get back to this in a moment. <o:p></o:p>
<o:p></o:p>
Alright so think of an motor is a big air compressor or pump. Its job is to suck air in compress it and expel it. Add in the correct mix of fuel and we have a motor. BUT fuel is what makes all the power in an motor so that means that the more AIR we have the more Fuel we can burn and the more power we can make. A good thing. But of have to keep the ratio of fuel to air correct ( actually ~13/1 makes the most power at the cost of some fuel economy) <o:p></o:p>
<o:p></o:p>
Also a motor is never 100% efficient. Besides heat lose in an ideal world a cylinder that displaces 500cc will take in 500cc of air each rotation of the crank and compress it. but due to restrictions in the intake track( intake manifold, air filter, boundary layers of air it’s a lot more technical than that but is not that important right now) a cylinder( unless forced induction is used ie turbo) will not pull in the full 500cc of air. in reality it will only pull around 400cc of air(~80%). So that means that our.5 L motor is accrual acting like a .4L motor. So how can we change this? Remove all restrictions. <o:p></o:p>
<o:p></o:p>
So we put a higher flowing air filter on. The cylinder is now getting 420cc of air per stroke instead of 400. That means more air we can now burn MORE fuel and make more power and get better efficiently. Same effect with a free flowing exhaust.<o:p></o:p>
<o:p></o:p>
So you are thinking we are burning MORE fuel how is that helping gas mileage. Glad you asked<o:p></o:p>
the motor is making more power and is wasting less power trying to pull air into the motor so less power is wasted. So that means the motor is NOT working near as hard to bring the car up to speed or to maintain speed so what you get(if you keep your foot out the gas) is BETTER GAS Mileage form a more efficient motor. <o:p></o:p>
<o:p> </o:p>
I can confirm that a K&N does NOT stop as much dirt as a paper filter but is does flow better and I never seen a motor that has worn out early because of a K&N filter( I have seen a lot). In my personal vehicles I run k&n just because I never haft to buy another air filter and it helps efficiency a bit . <o:p></o:p>
<o:p> </o:p>
Wow that was a long first post<o:p></o:p>
 
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SilverUberXeno

SilverUberXeno

El Tigre Blanco
Jul 26, 2005
4,620
26
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Long but appreciated, Bugman. There's a lot of good information in this thread. I've never heard of a motor going out early that had a K&N in it either. I suppose it comes down to how much filtration is necessary to protect an engine.

I'm willing to try a paper filter in comparison to the K&N for the sake of experimentation. Which one should I try? Based on the tables provided by Brandon's link, there are many good options. I think I wanna try the AC Delco, as that appears to be a virtual forcefield to dust particles. If I don't lose fuel efficiency with that thing, I'm golden.

As I understand it:

There is an ideal amount of air that an engine would like to have. This ideal amount (x) may not be reached using a conventional paper filter. However, if it is reached, there is no sense in INCREASING flow rate, since the engine will not use more than X even if it is available.

Correct?
 

bugman53

Well-Known Member
Aug 1, 2008
17
0
As I understand it:

There is an ideal amount of air that an engine would like to have. This ideal amount (x) may not be reached using a conventional paper filter. However, if it is reached, there is no sense in INCREASING flow rate, since the engine will not use more than X even if it is available.

Correct?

Correct. I also run k&n on all my stuff. Except my dune buggy.. that sand does bad things to a motor.
 

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