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So wait.... K&N air filters really just lots more dirt in your engine?

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KDOG

Diamond Member
Oct 9, 1999
5,558
8
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I saw a link in the sig of someone here (I forgot who they are now) that was to a test of air filters that seemed to show that K&N air filters really kinda suck - that they don't offer any appreciable boost in power and let something like 45X more dirt than standard filter. Is this true? I just recently got a K&N for my Jeep 4.0L I6. What do you think? Should I put the Fram back in? I do tow a camper a few times a year which is the main reason I got it, to squeeze as much power/efficiency out of the engine as I can.
 

mav451

Senior member
Jan 31, 2006
626
0
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I'd like to know the answer for this too. My colleague at work was raving about how much "extra power" he was feeling b/c of the K&N. He drives a stick VW - whereas...I have a '98 Avalon beater. So notwithstanding the Euro/Import angle, yeah I wouldn't mind more power, but I would be concerned if it's just letting more of everything through.
 

exdeath

Lifer
Jan 29, 2004
13,679
10
81
OEM paper filter is fine. 99.9% of stock engines on the road don't consume anywhere near enough air that the factory paper filter is a restriction. You need to be making some serious ponies and running a ton of boost before the filter becomes an obstruction (or have a poorly designed factory air box such that it doesn't use all the surface area of the filter).

Air filters do not make power. They can only impede power production when tons of other mods are brought into the picture that actually modify the engine and create a need for more air flow, particularly with any kind of compressor inlet.

Be wary of anything that claims to give you dyno proven gains as little as 5-10 HP; that's not even within the margin of repeatability error for a typical dyno!
 
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Tsavo

Platinum Member
Sep 29, 2009
2,644
37
91
Read it yourself:

http://duramax-diesel.com/spicer/index.htm

Snippet, gotta read the whole thing:

Compared to the AC, the K&N “plugged up” nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt.

K&N may allow the engine to develop more horsepower, but you'd be lucky to see 10HP...which is of zero benefit.
 

exdeath

Lifer
Jan 29, 2004
13,679
10
81
I suppose it is possible to see unintentional power gains from an aftermarket intake when the intake itself doesn't really do anything. MAFs are extremely sensitive, and changing piping and airflow characteristics of the inlet can skew the reading rich or lean. Your airflow volume hasn't actually changed, just the MAF output has changed due to change in plumbing, and if it skews rich it will cut fuel. Same air flow + less fuel = leaner mixture = more power, but it has nothing to do with the intake or an increase in airflow . You can do the same thing, albeit properly, with a SAFC type device (in fact manipulating the MAF/MAP reading with false data to trick the computer into changing the mixture without editing the fuel map is exactly how those devices work).
 
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Kalvin00

Lifer
Jan 11, 2003
12,705
4
81
Yeah, I believe it. I bought a K&N air filter for my motorcycle once and when I held it up to the light I could see through holes as big as a ball point pen tip.

I sent it right back and bought an OEM one...
 

PricklyPete

Lifer
Sep 17, 2002
14,714
164
106
Yes, more dirt is the general consensus on the internet...so it has to be right...it's science.
 

Gibson486

Lifer
Aug 9, 2000
18,378
1
0
K&N is made for performance vehicles....that is what they advertise. They let more air through, which increases combustion. To do this, you need to decrease filtration....which yeah, it counter productive for what you want in a consumer vehicle. Market the stuff right, though, the people will buy it. Whether it really gives a boost, i have no idea.
 

Throckmorton

Lifer
Aug 23, 2007
16,830
2
0
It's me!

When I bought my Jeep it had a K&N. I swapped it for a Wix paper filter. I believe Purolator is also a good brand.

K&N's own material says that the filtration performance can improve as it collects dirt. What does that tell you?
 

Stefan Payne

Senior member
Dec 24, 2009
253
0
0
Those open Filters are mostly crap, you don't have more horsepowers but less 'cause its suckin in hot air instead of cold.

And some engines already have an open filter...
 

JulesMaximus

No Lifer
Jul 3, 2003
74,182
635
126
My wife owned a BMW 3 series for a few years and I picked up a K&N filter for her car, this was years ago, and as soon as I dropped it in and started the car it threw a CEL. Put the paper filter back in and everything was fine. I took that K&N filter back to where I bought it and got a refund.
 

halik

Lifer
Oct 10, 2000
25,696
1
0
My wife owned a BMW 3 series for a few years and I picked up a K&N filter for her car, this was years ago, and as soon as I dropped it in and started the car it threw a CEL. Put the paper filter back in and everything was fine. I took that K&N filter back to where I bought it and got a refund.
Probably over oiled from the factory and it all ended up on your mass air sensor.
 

foghorn67

Lifer
Jan 3, 2006
11,883
49
91
I had someone do a back to back and back again oil analysis done. K&N was dirtier. Completely scientific? Nope. But this was just another reason not to.
 

sdifox

No Lifer
Sep 30, 2005
85,212
9,505
126
Isn't it easier to increase air box size + bigger filter surface area?
 

LTC8K6

Lifer
Mar 10, 2004
28,520
1,573
126
Given the comparative size of the air filter and the throttle body, why would you ever need more airflow than the paper filter can provide?

Unless you have dramatically increased the engine's ability to flow air, I can't see why you'd be worried about the stock paper filter...

The exception being operation in a particular environment.
 

Pacfanweb

Lifer
Jan 2, 2000
13,131
54
91
It's me!

When I bought my Jeep it had a K&N. I swapped it for a Wix paper filter. I believe Purolator is also a good brand.

K&N's own material says that the filtration performance can improve as it collects dirt. What does that tell you?
The filtration probably does improve, but their airflow advantage goes away pretty quickly.

Bottom line is, as mentioned before, the vast majority of mostly stock-to-stock engines don't need the additional airflow...can't use it. So all you're doing by adding a drop-in K&N is dirt to the engine.

A CAI is a different story entirely.....but even with one of those, I'd stick with another type of filter that actually FILTERS.
 
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