So far so good on the crankcase air filter. It seems more than adequate for the 4 CFMs that I'm pumping through there. Quarter Acre brings up a good point about what size the filters are. I did a little research on oil droplet particles that the filters are intended to filter and found they range in size from 3 microns down to 0.2 microns. I know that's not necessarily what these cheap amazon filters are but I would think it'd be a similar sub 10 micron size like the McMaster-Carr filters.