These #60775 Edelbrock Performer RPM Aluminum Cylinder Heads feature threaded inserts in the Rocker Shaft Bolt and Exhaust Manifold Bolt holes for superior strength and durability. They also feature Hardened Seats, Bronze Valve Guides, and fully machined Valve Cover Rails for a more consistent Gasket Seal. They offer improved power throughout the RPM range for greater Throttle response and top-end Horsepower. Equipped with Dual Valve Springs for use in Hydralic Roller Camshaft Applications up to .600″ lift. NOTE: Not recommended for use on the earlier 68-71 340’s with Factory 10.5:1 Compression Pistons…Use Our Part # EN0219A with 65cc Chambers for these instead.Cylinder Head SpecificationsCombustion chamber volume: 63cc.Intake runner volume: 171cc.Exhaust runner volume: 77cc.Intake Valve Diameter: 2.02″.Exhaust Valve Diameter: 1.60″.Valve stem Diameter: 11/32″.Valve Guides: Manganese bronze.Deck thickness: 5/8″.Dual Valve Springs: Yes, with Damper.Outside Diameter of Outer Valve Spring: 1.46″.Valve Spring maximum lift: .600″.Rocker stud: N/A.Guideplate: N/A.Pushrod Diameter: 5/16″.Valve angle: 18°.Valve Seat Machine Style: 3-Angle.Valve Seat Material: Ductile Iron.Exhaust Port location: Stock.Spark plug fitment: 14mm x 3/4 reach, Gasket seat.