Trick flow 175cc DHC small block chevy fast cast aluminum cylinder heads. These look like chevy double hump heads of the 1960s but much better and are a good pick for a 327 to 350 Cubic Inch operating below 6000 RPM. A356 aluminum/60cc chambers/straight plug/23 degree/min bore diameter 4.000″ 11/32 stem diameter stainless steel Int/exh Valve 2.020″/ 1.600″ Intake 175cc Exhaust 74cc both standard location CNC chambers 60cc Spring 1.470″OD Hydraulic flat tappet Valve Spring, 120 lbs on seat, .540″lift, Max RPM 6000 7°Chrome Moly Retainers 1.245″ O.D x .885″ I.D x .655″ I.D 7° Lock Valve Keepers Positive stop Valve Seals Guide plates 5/16″ Rocker stud 3/8-16 Special order 3-5 business days. Please e-mail with questions.