It greatly helps, when trying to maximize airflow through a filter, to have a large filtering area. But building a huge filter was a no go, it had to be small and very effective. This is where the Arlen Ness design artists started. Adding the inside surface of the air cleaner to the outside adds a huge amount of filtering area. With the integrated radiused air inlet this air cleaner showed some of the highest flow numbers that Ness ever tested. The final looks give the 65° air cleaners a very small custom and attractive velocity stack look that will effectively pull in the air from all sides. Filter elements are made from synthetic material. They resist water, a rain sock is usually not required. Filters are re-usable, just rinse clean and re-install. Oiling is not required. Note: Breather design is o-ringed at the heads, passes through the backing plate and is placed inside the mouth of the throttle body. This eliminates external breather hoses so nothing will be taken away from the clean look. Note: Not compatible with stage 4 64mm throttle bodies.