That engine series always intrigued me for some reason, maybe because of the odd-shaped valve covers. Here's some info if anyone wants to take the time to read it ...
W-series (Mark I) ....The first version of the "Big Block" V8 Chevrolet engine, known as the W-series, was introduced in 1958. Chevrolet designed this engine for use in passenger cars and light trucks. This engine had an overhead valve design with offset valves and uniquely scalloped rocker covers, giving it a distinctive appearance. The W-series was produced from 1958 to 1965, and had three displacement options:
348 cu in (5.7 L), available from 1958 to 1961 in cars, and in light trucks through 1964; 409 cu in (6.7 L), available from 1961 to 1965; and 427 cu in (7.0 L), available in 1962 and 1963.
The W-series engine was made of cast iron. The engine block had 4.84-inch (123 mm) bore centers, two-bolt main bearing caps, a "side oiling" lubrication system (the 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 the 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 cu in (4.3 and 4.6 L) "Small Block" engines, the W-series valve gear consisted of tubular steel pushrods operating stud-mounted, stamped-steel rocker arms. The push rods also acted as conduits for oil flow to the valve gear. Due to the relatively low mass of the valve train, mechanical lifter versions of the W-series engine were capable of operating at speeds well beyond 6000 RPM.
The combustion chamber of the W-series engine was in the upper part of the cylinder, not the head, the head having only tiny recesses for the valves. This arrangement was achieved by combining a cylinder head deck that was not perpendicular to the bore with a crowned piston, which was 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 plugs were inserted vertically into the quench area, which helped to produce a rapidly moving flame front for more complete combustion.
The theory behind this sort of arrangement is that maximum brake mean effective pressure (BMEP) 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 the trucks and heavier cars that were in vogue in the USA at the time. The W-series was a physically massive engine when compared to the "Small Block" Chevrolet engine. It had a dry weight of approximately 665 pounds (302 kg), depending on the type of intake manifold and carburetion systems present.
348 The first iteration of the W-series engine was the 1958 "Turbo-Thrust" 348-cubic-inch (5.7 L), originally intended for use in Chevrolet trucks but also introduced in the larger, heavier 1958 passenger car line. Bore and stroke was 4 1⁄8 in × 3 1⁄4 in (104.8 mm × 82.6 mm), resulting in a substantially oversquare design. This engine was superseded by the 409 cu in (6.7 L) as Chevrolet's top performing engine in 1961 and went out of production for cars at the end of that year. It was produced through 1964 for use in large Chevrolet trucks.
With a four-barrel carburetor, the base Turbo-Thrust produced 250 hp (186 kW). A special "Tri power" triple-two-barrel version, called the "Super Turbo-Thrust", produced 280 hp (209 kW). A "Special Turbo-Thrust" further upped the power output to 305 hp (227 kW) with a single large four-barrel carburetor. Mechanical lifters and triple two-barrel carburetors brought the "Special Super Turbo-Thrust" up to 315 hp (235 kW). For 1959 and 1960, high-output versions of the top two engines were produced with 320 hp (239 kW) and 335 hp (250 kW) respectively. In 1961, power was again increased to 340 hp (254 kW) for the single four-barrel model, and 350 hp (261 kW) when equipped with triple two-barrels.
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