The Edelbrock No. 60609 Performer RPM CNC Bare Cylinder Head has the same specifications as our popular Performer RPM cylinder head for 1962-79 389-455 c.i.d. Pontiac engines, but feature a CNC machined combustion chamber. The CNC machined chamber results in a consistent and precise chamber for improved flow performance. Performer RPM CNC cylinder head is available in two chamber sizes. The 87cc chamber version is ideal for 9.5:1 engines and will deliver excellent street performance on low octane fuel. The Edelbrock No. 60609 Performer RPM CNC cylinder head is patterned after the same port flange configuration as the 1969-1970 Ram-Air IV Pontiac Cylinder Head.