I use green foam (Code 3) right behind the supercharger. It filters well but has to be cleaned and oiled often. Actually I see bigger holes in my K&N filter but the K&N can go much longer between cleanings. As far as the Hepa filters, I would imagine the same thing, change them often. Look on the throttle body side to see if the dirt is getting through. If it is come up with plan B before you ruin your cylinders.