The Edelbrock #60989 E-Tec Cylinder Heads are replacements for 302, 327, 350 & 400 c.i.d. S/B Chevy engines with "Vortec-style" manifolds. They feature an LT1-style raised runner intake port design for increased air-flow and ultimate performance. A unique combustion chamber design positions the spark plug closer to the center of the cylinder, promoting a more efficient combustion resulting in more power. These heads include an adjustable rocker stud and guide plate set-up for use with adjustable rockers or washers to properly position the stud height to accommodate factory style self-aligning rocker arms. They have 20% more exhaust flow than cast iron Vortec heads, great performance up to 6000 rpm and can produce 9.5:1 compression with stock pistons in 350 cubic-inch engines. RPM E-Tec cylinder heads are dual-drilled and will accept 1987-95 centerbolt and/or 1986 & prior perimeter flange mount valve covers and most stock exhaust manifolds.INSTALLATION NOTE: • EQUIPPED WITH SPRINGS FOR USE IN HYDRAULIC FLAT TAPPET CAMSHAFT APPLICATIONS • Match with Edelbrock head gasket sets. • Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. • To use stock rockers on small-block Chevy heads, .100" longer than stock pushrods are required. Edelbrock pushrods #9629 are recommended. • Use Head Bolt Kits for easy installation. S/B Chevy heads may not be used on engines with less than 4" bore (262, 265, 283, 305, 307 c.i.d.) except with cams having less than .450" valve lift.