High Velocity Heads Super Sucker Carburetor spacers give you the midrange and high end benefits of 4-hole and open style carburetor spacers into one spacer. Originally designed for Winston Cup engines and eventually banned because of the performance advantage they provide. By increasing the velocity of the air as it transitions from the base of the carburetor to the intake valve you get more HP. The change in efficiency is so dramatic you may even need to make a jet change to the carburetor to maintain your air fuel ratio. Available in both aluminum and plastic, aluminum is for Circle Track or Street and Strip engines and plastic is for Drag Race only applications. Made In USA