The Edelbrock #607519 Performer Cylinder Heads are designed for 302, 327, 350 and 400 cid small-block Chevy engines up to 1986. These cylinder heads include your choice of 64cc (In order to retain stock compression ratio on 1970 and earlier small-blocks) or 70cc combustion chambers and high flow intake and exhaust ports. Complete heads include larger-than-stock 1.46" valve springs to handle most high-lift cams. These heads retain the stock intake port location for compatibility with standard manifolds and headers. Heat crossover is machined for 50-state emissions legal performance.INSTALLATION NOTE: • EQUIPPED WITH SPRINGS FOR USE IN HYDRAULIC FLAT TAPPET CAMSHAFT APPLICATIONS • Match with Edelbrock head gasket • When using hot air choke Q-Jet carbs and Performer manifold with above heads, choke kit #1932 is required. • Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat.