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 center bolt and/or 1986 & prior perimeter flange mount valve covers and most stock exhaust manifolds.