Well...I put a K & N on my 84 300SD and after 30K it started smoking like crazy. Head & valves were fine but compression was shot in a couple of the cylinders. I don't know if I can blame the filter, the engine had 320K on it, but it makes sense now. I read a couple of K & N threads here and got enough nerve to run the K & N on my 83 300SD for a about a thousand miles, and then switched to the stock filter. No difference in power or mileage I could detect, but it sounded more powerful with the K & N. I like the idea of a re-useable filter, but will not donate another engine.

How about a foam pre-filter on the outside of the K & N filter...I have seen these on some high performence air filter systems?

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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car