I replaced stock filter with a K&N and clean it with their solution ,then reoil it as instucted. If intake is dirty before turbo its like intake on all our equipment. Its not gritty dirty just ,well a huge amount of air goes through it each minute ,same with our backhoe diesel and you can find a light film at the intake on it also. Just curious where all this bad info comes from on filters because I find even on our commercial gas motors a dirty film before the throat going in but, we run our stuff all day. I mean you have lubrication in heads ,combustion and a lot of heat ,and my guess is you will always have a threshold of particles that are burned up that doesnt mean its going to score cylinder walls or damage valves. Incidently just a week ago I popped out my K7N filter and alonside it a mouse had built a nest. The mouse chewed the wires on the outside of filter and gave up trying to chew its way through the filter. Had that been a paper filter I would have had catestrophic failure by sucking all that into inner cooler and turbo. Mouse did the same thing on a VW diesel motor I had and instantly sucked everything into the intake and heads. I junked the car for lack of time to tear it down but the mouse had chewed all the way through the paper filter and had a big nest. Anyway.
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