The Flow Control System utilizes a specially designed base in combination with a unique lid, featuring a tongue or protrusion, that reduces intake turbulence. The resulting smooth, laminar flow enhances cylinder filling, horsepower, and torque. The filter element is the world famous K&N Filtercharger for the ultimate in airflow and filtration. The result of this powerful combination is a typical 20 HP increase on a 350 CID engine.The inspiration for this particular air cleaner was the 390 CFM Holley. Many tracks and racing organizations use this carburetor as a restrictor. It flows plenty on the 390 CFM and you can pass it all the way up to the mighty 850 CFM and it keeps on making horsepower. Available in two sizes and complete with all parts necessary for installation.