Edelbrock part #15643 is a Supplemental Fuel Pump Kit is required for GM trucks and SUV's utilizing #1564 Edelbrock Supercharger Systems. Locate your Vehicle Identification Number (VIN). Verify if your vehicle requires a supplemental fuel system upgrade. If digit 8 of your VIN (Engine Type) is represented by a C or J, your vehicle will require a supplemental fuel system. Now identify what Body Type your vehicle is by verifying VIN digit 7. Vehicles with a 2 or 6 will use the long wheel base kit #15643. This system is not needed and will not work on Flex Fuel models as Flex Fuel vehicles come standard with adequate fuel systems.