About air filters:
I flew a while with a cheap foam filter,
Sounds like a UNI-Filter. I used to use them on my modified Ski-Doos when I was too poor to afford the K&N. They work OK.

 
So keep those filters from collapsing.
 I was concerned about this, so I built a vacuum relief valve, which is an integral part of my filter box. In the unlikely event of a filter plug due to dirt or more likely ice, it will simply overcome the spring pressure and allow unfiltered air from inside the cowl to flow. I probably won't even know if it has opened.

S. Todd Bartrim
Turbo 13B rotary powered
RX-9endurance (FWF)
C-FSTB (reserved)
http://www3.telus.net/haywire/RV-9/C-FSTB.htm

        "Imagination is more important than knowledge"
                                        -Albert Einstein