This head is based on Edelbrock's Performer RPM aluminum head for 1963-1968 427 Ford FE Low and Medium Riser engines (4.23" dia. bore size) but with no port profiling or bowl blending ports. It is engraved with the NHRA Logo on both ends to help verify its legality. It has machined 76cc combustion chamber similiar to a Ford medium riser combustion chamber and the 8-bolt vertical exhaust flange bolt pattern. This head is sized for 2.09"/1.66" valves for 427 low riser applications. For 427 medium riser applications the head must be prepared for the 2.19"/1.73" size valves used in 427 medium riser engines.