Edelbrock has expanded its line of small-block Chevrolet cylinder heads to include the new Performer RPM Cylinder Head designed specifically for small-bore engines.The new Edelbrock Performer RPM Small-Bore Cylinder Heads are engineered for use with 265, 283, 305 and 307 cubic-inch small-block Chevy engines produced from 1954-2003 with bore sizes less than 4.000 inches. To accommodate the smaller bores, valve spacing on these heads have been reduced to 1.817 inches while maintaining the early-style Gen 1 (1959-86) valve cover bolt pattern so that you can use your favorite small-block Chevy valve covers. These new Performer RPM heads also retain the stock straight spark plug angle and exhaust flange bolt pattern for ease of use with factory-style exhaust systems.Edelbrock Performer RPM Small-Bore Cylinder Heads are legal for use on pre-pollution-controlled vehicles only. Available bare (#61009), with springs for flat-tappet (#61019) or with springs for hydraulic roller camshaft (#61015); these heads can also be used with larger-bore engines if desired.Like all other Edelbrock Performer RPM series cylinder heads, these feature a thick 9/16-inch deck, extra-thick port walls, high-flowing ports, ductile iron seats, one-piece stainless-steel valves, and high-quality rocker studs. Edelbrock cylinder heads also feature state-of-the-art compact combustion chambers and highly efficient ports that offer improved performance and great throttle response throughout the rpm range. Other top-quality features include threaded inserts for rocker studs and exhaust bolts for superior strength and durability, as well as manganese-bronze valve guides. These cylinder heads are designed in-house, cast from A356 aluminum, heat treated to T-6 specs, and machined in Edelbrock’s Southern California USA manufacturing facilities for unsurpassed quality and performance.