Various filter research I've read indicates that the K&N flows better than paper but catches less dirt. I have looked but haven't found definitive reports showing the effectiveness of oil bath vs paper. I know that heavy truck applications went to paper later than cars and that optional heavy service air cleaners on truck tended to be oil bath well into the sixties. They are certainly messy and time consuming to renew compared to changing a paper filter. Oil-bath cleaners would be more expensive to manufacture also. I have two carbs with oil-bath cleaners and they kept the previous engine clean for ~200,000 miles till it burnt a piston. I clean them once every couple of years or when there is dirt in the bottom of the oil bath, maybe 15,000 miles or so.
