To K&N or not to K&N that is the question...

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Jan 10, 2006
SW Florida
Well what do you guys think, on the turbo diesel truck forums the guys all say no way, (to much dirt allowed) but I want to see if you guys think it is worth anything.
hoser said:

Wow, that's a pretty damning report (of K&N).

Anybody know of other independent test reports to corroborate the above? (Any test report may be fabricated, fully or partially...)

I wonder how K&N got so big, in aftermarket selling pricey filters, if their filters are so poor? Seems like many others also would have uncovered this and gotten the word out, by now, if true.
Another no vote from me.
Guess I outta think about bolting the stock air box back in...

Good thing I kept it.

If anyone wants an independent report, get a used oil analysis done with your stock filter, change out to a K&N and run the same mileage and get another UOA done. Repeatedly, and I mean over 90% of the time repeatedly, more dirt is allowed into the engine.

K&N got so big because of performance claims, not claims of superior filtration. They do allow an engine to breathe easier, which can help produce more power, especially on a modded engine still using a stock filter box. On most stock vehicles the gain is negligible and mostly placebo effect. There can be some gain (say 3% or so) but nothing worth letting dirt in for IMO. K&N's are also notorious for screwing up vane type mass air flow sensors by gumming them up if the filter has excess oil on it.

Mac: Uh-huh and uh-huh to that.
Yet another NO from the peanut gallery (A.K.A. sincity100 )
NOPE, used it on my bimmer, it allowed grit and dust past the filter and I had to clean the inside of the MAF. Absolute garbage..
(Tinkerer scratches head...K&N not good?...hmmm)

So, any opinions on best paper-type filter for 100? (OEM from Toyota Dealer, or something else?)

The report at

doesn't include Toyota (or Denso, or whoever actually makes the Toyota OEM).

(Not sure whether Delco - Delphi now, right? - makes one that fits the 100; the above report seems to favor a Delco filter of some kind...)
I previously used the K&N filters on both my Porsche Boxter and Cruiser, but no longer use them. Here's why.

On the Porsche the air flow sensor is down stream and literly below the filter. Too much oil on the filter and it can drip down onto the sensor affecting its readings. Not good.

On the Cruiser I performed a simple test, after reading the article referenced earlier. Used a clean cloth and wiped out the intake above the filter. Went wheeling for a couple of days and when I got back wiped the area again with a white cloth. Found very fine dust residue that made it past the filter. :mad:

Did the same thing after replacing the k and N with a stock paper filter. No dust. That did it for me.

I'm using stock filters in both vehicles now.

I think I remember Consumer Reports liking the Fram Filters.
Tinkerer said:
(Tinkerer scratches head...K&N not good?...hmmm)

So, any opinions on best paper-type filter for 100? (OEM from Toyota Dealer, or something else?)

The report at

doesn't include Toyota (or Denso, or whoever actually makes the Toyota OEM).

(Not sure whether Delco - Delphi now, right? - makes one that fits the 100; the above report seems to favor a Delco filter of some kind...)

Ditto on this, what is the best available filter for the 100?
Dealer or otherwise...
Geez, I only have 24k on the 100. I guess I still have time to put the stock air boxes back in 'for I fawk it up.
I have used K&N in the past, but no more. The reason they sell a lot of filters is because they have better airflow. However, that comes at the sacrifice of allowing dirty air to get by.

I prefer Toyota OEM filters. They are reasonably priced for the performance and are discounted by dealers several times a year.
NO .. when i purchase one for my LC .. the E-Choke become so dirty and made the idle above 1100 RPM .. in that case you must clean it ..

Stick with OEM Filter with the snorkle ..
lizardking100 said:

I'm not a scientist, but I understand that our atmosphere is a homogenous gas mixture. The purpose of the air filter is to catch as much particulate matter as it can while maximizing the flow of air. So here is my question: Given that an air filter relies up physical properties (as opposed to chemical or ionic) to restrain particulate matter. Doesn't there have to be a negative correlation between air flow and the capture of particulate matter? It seems that way to me, but does anyone know for sure?

[Another short essay below - blame the coffee.]

The correlation is not necessarily negative. It depends on many things in the filter design.

For a given design family in a given size envelope with same-size inlet & outlet flow paths etc, it is generally negative - more particulate captured, > more restriction.

But filtration mechanisms are not just simple physical entrapment, as with a plain paper filter.

For example, ancient automotive air filter designs included oil bath types that had no filter media element whatsoever, but rather, relied on a combination of vortex physics and a shallow oil bath, to sling particulate out of the airstream and capture it in the oil.

The vortex concept is used in other stationary and mobile applications also. It's a way to drop the bigger particles out of the airstream before the stream reaches the final filtration stages of the assy.

There are also other filtration concepts altogether - stuff such as electrostatic filtration, etc.

Even within the plain paper element family, there are many variables for a given size filter that affect efficiency and flow restriction, such as pleat pitch and depth, media, etc.

Ultimately, the only way to know is to test. (Honestly)

That's why I'm wondering if anyone knows of other controlled, unbiased, truly scientific tests to corroborate the K&N-damning test linked earlier in this thread. That's the only way to do science (peer review and test replication & publishing).

(Even an honest single person - single experience, reported in good faith, like the example of the K&N leaving more dust in the intake than the OEM filter, may be misleading: There are a lot of variables that might have yielded that result, including actual ambient dust levels encountered, K&N properly oiled or not, measurement error, etc....)

K&N will claim that their filters can flow with less restriction yet still capture adequate % of particles because they employ a light oil in the foam as the design concept. (Oil assists the particle entrapment)

This will certainly introduce some small amount of oil into the air that passes through the filter. That oil (vapor/aerosol) will create slight oil deposit in the remainder of the intake system, and that in itself will also trap some of the remaining particules passing into the intake, inside the intake passages. Is this a problem? If it is excessive, definitely (as where it fouls the MAF etc.). If it is slight - maybe not.

The K&N oil vapor that passes into the filtered airstream will start out at a high rate, then gradually decline as the filter is used, to nearly zero after some time in service. So testing a freshly-oiled K&N will give different results than testing one with 50k miles on it, both with respect to filtration properties and also with respect to oil vapor left in the filtered air and related issues.

I'm not a K&N fan - I'm just looking for hard data, test results, to help find the best filter for this particular filter box.

More input welcome.
(Another "chapter" - the last one is long enough as it is by itself...:)

Quick reads from K&N site:

"Our goal is to design our air filters to achieve maximum airflow while targeting overall filtration efficiency at 98%"

"K&N air filters generally achieve overall filtration efficiency in the range of 97% - 98%, while some of our air filter designs have achieved levels as high as 99%. "


This generally agrees with the K&N-damning report that found K&N filtration efficiency was "96.8%"



1. K&N says (and I agree) that test results will vary not only by specific filter spec (filter type, size & vehicle application - the "box"), but also for different filter samples within one specific filter spec.

So testing only one filter sample, in one application, is not enough. You need more data.

2. I gotta say, that when I see test results like those at

that report test results like "98.73 %" efficiency (Purolator), I reach for a big grain of salt. Such testing, of only one sample filter, is not exact enough to report 4 significant digits (2 decimal places here). Usually this is a sign of untrained testers. (Or dishonest testers attempting to convey a false appearance of precision in their results.)

There is way too much error inherent in such testing to report 4 significant digits.

3. Another problem with the SPICER.htm test report is the way they present the bar graphs: 97 % to 99.x % is not a very large range, but the graphs make it appear to be a HUGE difference. This is a common reporting distortion technique, and makes me wonder if the reporter is truly unbiased, or pushing his own agenda (paper).

I'm not saying the SPICER.htm test is not valid, but I sure would like to see more unbiased independent tests, of multiple filter samples & models/applications.

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