Well DC, since you have alot of experience with VW diesels and turbo diesels, lets look at what some owners of Dodge Trucks equipped with Cummins turbo-diesels have had to say about K&N air filters:
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Posted by: Gary C
I was talking to my off-road friend today and he says hardly anybody uses a K&N filter any more for off-road. So I asked why, he said it was simple, he said take out your drop in K&N and hold it up to the sky and tell me what you see. I told I would do it in a bit. So later on I pulled the filter out and held it to the blue sky and saw 1000's of little holes in the filter, I would think that dirt is a lot smaller and would easily pass through these small holes. I grabbed the stocker filter and threw it back in.
The truck with the K&N ran better and and notice an increase in fuel mileage instantly. But it is not worth the cost of a new motor.
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Posted by: Lee Weber
EZ, I have to agree with you about the value of holding a new K&N up to the light. IMHO, K&N has a major quality control problem, which is at the root of this controversy. I use K&Ns in my 2 gAssers, because they definitely give a couple of mpg increase with naturally aspirated engines. But the last one I bought didn’t pass the eyeball test described by Gary. I took it in to the lab and checked it out with a dissecting microscope and found that many of the holes were greater than 100 microns. Now that will pass dirt regardless of the oiling state. I exchanged the filter for another that pAssed both the eyeball and microscope test. So there are some bad ones out there but the rest are fine.
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Posted by: Mundgyver
Gotta love them K&N boys. They tout the fact that their filters will flow more air and will give more power. This be true! Only problem is, they don't tell you about how thin the filtering is. I got a friend that went through two MAS-FLOW units at $600 a pop before he figured it out. Stick with the stock or go to the AMSOIL.
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Posted by: Vaughn MacKenzie
I had a bad K&N. Silicate level was 15 on my oil sample when running it, then dropped to half that when I put the Amsoil in. I got tired wiping the dust out of the inside of my intake hose.
I think most K&Ns are good and do the job, but there are bad ones out there and you won't catch me using one again.
Vaughn
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Posted by: ROAD WARRIOR
I totally agree with Gary on this subject. I had a friend who put a K & N in his Banshee and went racing in the local quarry. He said after a couple of hours he noticed a big loss in power. He lifted up his seat and to his surprise there was a quarter inch of gravel dust laying inside of his beloved K & N. -------------------------------------------------------------------------------------