Attached pdf shows some interesting testing on air filters, OEM vs K&N. Thought it might be interesting 

air filter test.pdf

Very interesting - thanks for sharing, I would be interested to replicate those pressure drop experiments with more filters across the range to include oil free varieties.

Nothing to do with the research but they could do with addressing the layout of the main text, increase the line spacing and put a whole space between paragraphs - massive wall of words made it quite hard to get through.