Chevrolet Big-Block Engine - Generation 1: "W" Series

Generation 1: "W" Series

The first ever production big block V8 Chevrolet engine was the "W" series, released in 1958 for passenger car and truck use. This engine was an Overhead valve design, with offset valves and unique scalloped rocker covers, giving it a distinctive appearance. The "W" series was produced from 1958 to 1965, with three displacements offered: 348 cubic inches (5.7 L), available from 1958 to 1961 in cars and through 1964 in trucks; 409 cubic inches (6.7 L), available from 1961 to 1965; and 427 cubic inches (7.0 L), available only in 1963.

As was the norm at the time, the "W" engine was of cast iron construction. The block had 4.84-inch (123 mm) bore centers, two-bolt main bearing caps, a "side oiling" lubrication system (main oil gallery located low on the driver's side of the crankcase) with full flow oil filter, and interchangeable cylinder heads. Heads used on the high performance 409 and 427 engines had larger ports and valves than those used on the 348 and the base 409 passenger car and truck engines, but externally were identical to the standard units. One minor difference between the 348 and 409/427 was the location of the engine oil dipstick: it was on the driver's side on the former and passenger's side on the latter. No satisfactory explanation was ever offered for why this change was made. However, it did provide a fairly reliable way to differentiate between the smaller and larger versions of the engine.

As with the 265 and 283 cubic inch small block engines, the "W" engine valve gear consisted of tubular steel push rods operating stud-mounted, stamped steel rocker arms. The push rods also acted as a conduit for oil flow to the valve gear. Due to the relatively low mass of the valve train, mechanical lifter versions of the "W" engine were capable of operating at speeds well beyond 6000 RPM.

Unlike many of its contemporaries, the "W" combustion chamber was in the upper part of the cylinder, not the head, the latter having only tiny recesses for the valves. This arrangement was achieved by combining the use of a cylinder head deck that was not perpendicular to the bore with a crowned piston, a novel concept in American production engines of the day. As the piston approached top dead center, the angle of the crown combined with that of the head deck to form a wedge shaped combustion chamber with a pronounced quench area. The spark plug protruded vertically into this chamber, which tended to cause a rapidly moving flame front during combustion.

The theory behind this sort of arrangement is that maximum brake mean effective pressure is developed at relatively low engine speeds, resulting in an engine with a broad torque curve. With its relatively flat torque characteristics, the "W" engine was well-suited to propelling both trucks and the heavier cars that were in vogue in the USA at the time of the engine's development.

The "W" had a dry weight of approximately 665 pounds (302 kg), depending on intake manifold and carburetion, and was a physically massive engine compared to its small block predecessor.