Let me repeat that in dusty conditions, an oiled foam filter is better than a dry paper filter.

Even the aeroplane industry agrees - you know, the one where everything has to be tested and retested, and documented.

Here's the Pilatus Porter PC-6:

http://www.pilatus-aircraft.com/#2

Their "desert kit" consists of a box with oiled foam filters rather than the ordinary, smaller filters they use. They don't do this to add more air to the aircraft's turbine intake, but to stop ingress of sand and dust.