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One of my bikes came (used) with K&N pod filters and I found a scary amount of grit on the 'clean' side of the filter, collecting on the inside of the intake tubes and presumably also going through the motor. No thanks, not for me. I have a few K&N filters I have taken off used cars and can see pinholes in them when they are held up to the light.
There are a few tests out there, here is one:
http://duramax-diesel.com/spicer/index.htm
A fleet test in a quarry was also interesting. I do not have a link to that one.
A filter should filter, screw the extra HP if it's indeed even there.
-Joel.
Joel Frahm
1992 968 Cabrio Black/Cashmere
1994 968 Cabrio Iris Blue/Lt. Grey - Supercharged
1987 928S4 Diamondblau/Blue
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<!--quoteo(post=76248:date=Jul 28 2009, 06:20 AM:name=PorscheDude)-->QUOTE (PorscheDude @ Jul 28 2009, 06:20 AM)
<{POST_SNAPBACK}><!--quotec-->Your concerns are valid.
If one is lazy, then use a paper filter.
If one is a fanatic about keeping things tidy, then there are
no worries.
Reports of problems are very few among all autos, more than likely those reported faults were from idiot owners
who did not properly maintain the filter.<!--QuoteEnd--><!--QuoteEEnd-->
Agreed on idiot owners. Had a friend who cleaned his K&N the other day, unfortunately when I came to his place he was already done, using pressurized air and some kind of solvent for cleaning greasy engine parts. Afterwards he rinsed the filter from both sides with the maximum pressure of hot water from the tap. It was "How To Destroy Expensive Filters 101".
This being said I am reluctant to use filters that I haven't bought and maintained myself.
1995 Riviera blue 968CS with LSD, custom LEDA coilovers with t-bar delete, S4 brakes, RS Barn braided lines, Tarett sways, Racers Edge bushings everywhere, Rack Tack, Design 1 braces and short shift kit, air box mod, RS Barn stage 1 chip, RS Barn cat back, RUF BTR2 wheels with Toyo R888, Deutsch Nine TRS version 2 rear wing (carbon fiber), AIR repop splitter (carbon fiber), brake cooling intakes (carbon fiber), Sparco seats and belts, OMP steering wheel and a lot of other little things that I can't recall at the moment...
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<!--quoteo(post=76251:date=Jul 28 2009, 02:00 AM:name=firefish)-->QUOTE (firefish @ Jul 28 2009, 02:00 AM)
<{POST_SNAPBACK}><!--quotec-->Agreed on idiot owners. Had a friend who cleaned his K&N the other day, unfortunately when I came to his place he was already done, using pressurized air and some kind of solvent for cleaning greasy engine parts. Afterwards he rinsed the filter from both sides with the maximum pressure of hot water from the tap. It was "How To Destroy Expensive Filters 101".
This being said I am reluctant to use filters that I haven't bought and maintained myself.<!--QuoteEnd--><!--QuoteEEnd-->
I disagree that the care of the filters is a big issue. Compressed air might make little blowholes in the filter, but generally I think it is the nature of the gauze media that allows it to pass harmful particles.
As I understand it, the way a K&N works is that you have a several layer weave of cotton gauze, which is carefully oiled to make the threads sticky. When a particle passes through it, it probably strikes a string or two and usually sticks to one of them. Sometimes (one or two % of the time) it does not get stuck and moves on through. A standard filter, on the other hand, is made of a material that should not have any holes in it big enough for a harmful particle to pass through, the fibers being much smaller and more randomized.
The nature of the K&N media is such that there is more likely to be pathways through it that encounter few strands of the cotton string.
Less restrictive, sure, but more likely to pass some dust. I live in a dusty environment. Pass.
K&N's own spiel is that the filter gets more effective as it loads up, if that does not indicate that holes in the filter are getting plugged up with dirt and dust I don't know what does.
Anyway it's your motor. Performance has it's cost.
-Joel.
Joel Frahm
1992 968 Cabrio Black/Cashmere
1994 968 Cabrio Iris Blue/Lt. Grey - Supercharged
1987 928S4 Diamondblau/Blue
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Rereading that Duramax test, I converted the units to try to quantify the restriction difference between the K&N and other filters. The most restrictive filter showed 6.23 in H2O restriction and the K&N was the least at 4.54 in H2O at 350cfm (350cfm is pretty close to a 968's requirements at full honk.)
Converting those numbers to psi, I find the pressure difference between those two filters is .009 psi. Really? That is pretty tiny.
The interweb tells me "1 PSI is equal to 27.6807 INH20 @ 4 C" so a hundredth of a psi sounds possible, and it's looking like the pressure drop for a filter is not really much to write home about. 0.10 psi might mean something but 0.01 psi, not so much. If we were making 237 crank hp at 14.7 psi that's about 16 hp per psi, so 1.6hp IF we could prevent a .1 psi pressure drop. 0.16 if we only got 0.01 psi.
So what is on the table? Maybe as much as 3hp between running a filter and going commando. But from the Duramax test and the bobistheoilguy test it looks like the K&N is allowing 0.01 or 0.02 more pounds of pressure in the airbox over a stock-type paper element, or (roughly) 0.16 to 0.32 crank HP.
I would not use a K&N even if it netted 2 HP, which I think is not real likely, being 10x more than the data suggests.
It'd be interesting to get a handful of MAP sensors and try to measure it though myself. One could also try to see what sort of ram air effect we can get too. Might be in the error range for a MAP sensor though... might need manometers in the cockpit instead. I do have a four-stick mercury one for motorcycle carbs. Hmmm.
I guess there is a reason why they use manometers and not pressure gauges for this sort of test. They need the resolution down to a thousandth of a psi to measure anything.
-Joel.
Joel Frahm
1992 968 Cabrio Black/Cashmere
1994 968 Cabrio Iris Blue/Lt. Grey - Supercharged
1987 928S4 Diamondblau/Blue
