Intended for installation on 1965-1976 Small-Block Oldsmobile 350-403 c.i. engines equipped with a flat tappet camshaft these 356-T6 aluminum casting cylinder heads (PN61039) are a modern refinement to our PN6051 heads except they can accommodate a factory-style mechanical fuel pump. A smaller 68 cc combustion chamber achieves a more appropriate small block compression ratio compared to our PN61025/61029’s larger 77 cc chamber which yields a lower compression ratio than most engine builders desire on a small block engine. These heads require a 3.9375” minimum bore and feature a modern chamber design with optimized spark plug positioning. Maximum airflow is achieved through the factory 6-degree valve angle using high-flow 200 cc intake and 130 cc exhaust port volumes along with 2.072” intake and 1.680” exhaust valve sizes in their O.E. positions. A finished deck thickness with added material above the intake port and pre-counterbored head-bolt holes for .5” diameter studs provide extra clamping force in key areas. A stud-and-guide plate valvetrain system (as opposed to the O.E. pedestal type) provides a solid foundation for the beefier diameter pushrods and Helicoil inserts in the exhaust and rocker stud holes keep bolts secured. However there are no provisions for a heat crossover. Although these heads will fit on Big-Block Oldsmobile engines the 68-cc combustion chamber size is not ideal for a big-block application as it will raise compression. See PN 61025 and PN 61029 for big-block specific cylinder heads.