The Citation, Omega, Phoenix and Skylark use two different engines, an inline four cylinder built by Pontiac as standard equipment, and a V6 built by Chevrolet as optional equipment.
The 2.5 liter (151 cu. in.) four cylinder has been in production for many years. The cylinder head and block are lightweight iron castings. Five main bearings support the crankshaft, which is made from cast nodular iron. In 1979, Pontiac updated the cylinder head design to a crossflow configuration; in the X-Body cars, the intake manifold is at the rear of the car and the exhaust manifold is at the front. A crossflow design permits better scavenging of gases and more efficient combustion. The intake manifold is made from cast aluminum, and has an integral passage through which engine coolant circulates, providing faster warmup and lower exhaust emissions. An EGR port is cast into the manifold, receiving exhaust gases from an internal passage in the head. The cylinder head has integrally-cast straight valve guides. Ball-pivot rocker arms are operated by pushrods driven by the camshaft through hydraulic lifters. Zero lash is maintained by the lifters, which require no periodic adjustment. Three ring cast aluminum pistons are connected to the crankshaft by Armasteel connecting rods. Camshaft drive is taken from the crankshaft by a bakelite fabric composition gear; the crankshaft gear is cast iron. One feature of the engine appreciated by do-it-yourselfers is the inclusion of pushrod covers on the side of the engine, which permit lifter replacement without removal of the cylinder head.
The Chevrolet 2.8 liter (173 cu. in.) V6 is an entirely new design. Most striking is the 60° bank angle of the cylinders. This design creates a more compact engine layout than the conventional 90° V bank arrangement. A 60° layout is also inherently better balanced when used with six cylinders, since a 120° firing order results naturally, providing harmonic balancing without the need for special and less satisfactory crankshaft configurations. In other respects, the Chevrolet V6 follows the conventional design of the highly respected smallblock Chevrolet V8. The cylinder block and head are cast from iron. The cast nodular iron crankshaft is supported by four main bearings; number three is the thrust bearing. Camshaft drive is taken from the crankshaft by a conventional 3 / 8 inch pitch chain and splintered iron sprockets. Ball-pivot rocker arms are used, mounted on individually-threaded studs. The rocker arms are driven by pushrods actuated by zero-lash hydraulic lifters. Pushrods are located by a guide plate held under the rocker arm stud. The intake manifold is cast from aluminum, as are the water pump and pistons. Connecting rods are made from forged steel.