Butler Performance Inc. - Rd-Port Cylinder Heads (Out-of-the-Box) Edelbrock
Edelbrock Performer RPM heads produce outstanding horsepower with excellent low speed torque and throttle response. Designed for 1965-79 389-455 c.i.d. Pontiac engines, these heads are patterned after the 1969 -70 Ram Air IV Pontiac cylinder head. Two styles are available: a street legal 87cc combustion chamber version for low compression applications using 92 actane fuel and a 72cc chamber version for higher compression, racing applications. Both heads have Ram Air IV exhaust port flanges.
" When using a Pontiac 350 block, 1.66" exhaust valves are required. Also, the 62-64 will require 65 and up or aftermarket intake and 67 and up pistons with valve pockets for 14-degree heads. The top of each cylinder bore may need additional notching to clear higher lift cams- this must be checked before installation "
**Picture below shows the exhaust port shape of Edelbrock RPM heads that require ROUND PORT headers**