The AFR Emissions Legal (versions from 1969-94 with heat riser, CARB EO #D-250-2), 180cc intake port small block Chevy cylinder heads are available in your choice of straight, or L98 angle plug versions. These heads feature a 75cc or 65cc combustion chamber with a 64cc exhaust port and a 3/4” thick head deck (ideal for nitrous or blower applications.) Standard valves are 2.020 intake and 1.600 exhaust with AFR’s hardened ductile iron interlocking valve seats. The exceptional flow characteristics, ideal operating range of idle to 5500 rpm (higher rpm ranges possible depending on combination of parts), 23º valve angle, and standard valve spacing make this the perfect street aluminum cylinder head for 327 cid to 350 cid engines from 1955-86. Also available for 1987 to present engines with center bolt valve covers and 2 center intake bolts at 72º angle. No special parts are required. Vortec style head available too. Dual valve cover bolt pattern is standard. Exhaust port is raised .100 over GM L98 cylinder heads. Note: Hydraulic roller cams typically experience valve float at 6000-6200 rpm because of their fast ramp rates. AFR suggest you upgrade your springs to AFR part #8047, 1.290 O.D. with higher spring pressures and use our Patented “Hydra Rev Kit” to reduce chances of valve float associated with rpm 6200 or higher. Chevrolet Small Block - 180cc CNC Street Ported Heads - 65cc Combustion Chambers, Straight Plug - Fully Assembled