PERFORMANCE INDUCTION STACKMade to increase engine performance by improving the airflow in the carburetor. This Performance Induction Stack is designed to simply bolt on to most Holley 4 bbl. Carburetors and provide a real performance boost. It can be used alone or in conjunction with most air cleaners, provided there is adequate (2" min.) clearance between the stack and the air cleaner top. Tests with a 780 Holley carburetor have shown this unit to increase airflow by up to 5% over competitive products.