Cylinder Head Specifications: Combustion chamber volume: 70cc / 64cc; Intake runner volume: 185cc; Exhaust runner volume: 60cc; Intake valve diameter: 2. 02"; Exhaust valve diameter: 1. 60"; Valve stem diameter: 11/32"; Valve guides: Manganese bronze; Deck thickness: 9/16"; Valve spring diameter: 1. 460"; Valve spring maximum lift: . 550"; Rocker stud: 3/8" with guide plate; Guide plate: Hardened steel; Pushrod diameter: 5/16"; Valve angle: 23°; Exhaust port location: Stock; Spark plug fitment: 14mm x 3/4 reach, gasket seat Use with Hydraulic Flat Tappet Camshafts . 550" max lift. (NOT Compatible with Hydraulic Roller Camshafts) Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. Requires hardened pushrods. Not legal for sale or use on pollution controlled motor vehicles.