Chevrolet Big Blocks W series—The First Generation


Chevrolet made a small-block, starting in 1955, that was very popular and quite serviceable for a few years, but the cars kept getting a little bigger and a bit heavier. The time was right, though, and in 1958 Chevrolet introduced the first big-block V8 for a passenger car, the “Single U” series with offset overhead valves and unique scalloped rocker covers. The more versatile“W” series, also introduced in ’58, started with the 348-cubic-inch (5.7L) made until ’61 for cars when the 409 cubic inch (6.7L) and the 427 cubic inch (7.0) took its place.

The 409 was an option until 1965, but the latter 427 was only available for ’62 and ’63. The W block series was a traditional cast-iron block with 4.84-inch (123 mm) bore centers, two bolt caps for the main bearing. Lubrication was the “side oiling” type with the main oil reservoir located low on the driver’s side of the crankcase, a full-flow oil filter, and cast-iron heads that were interchangeable with other W series.

The high-performance 409 and the 427 valves and ports were larger than the 348 was, but externally all are identical other than the dipstick was on the driver’s side in the 348 but on the passenger side in the higher performance engines. There’s no reason for the variation, but it was an almost infallible way to tell them apart. The tubular steel push rods activated the stud-mounted stamped steel rockers and were a similar design to their small-block predecessors. The push rods do double duty by supplying lubricating oil to the valve gear. The W engine mechanical lifter versions ran true even beyond 6000 rpm thanks to the low mass of the valvetrain.


The “W” engine was unique in that the combustion chamber is entirely in the block with the heads sitting flush; there are only small indents for the valves to seat without touching the piston top. Another distinctive feature to make this configuration copacetic was putting a crowned piston into a bore that wasn’t perpendicular to the cylinder head mounting. When the piston approaches top dead center, the head deck and the crown angle combine to form a wedge-shaped combustion chamber with the spark plug vertically protruding into this quench area forcing the flame produced to move quickly during the combustion stroke.

The theory motivating this configuration is maximum brake mean effective pressure develops at lower rpm, which gives the W engine a wide torque curve. This engine is ideal for the heavy passenger cars and trucks that were the norm for this era. Compared to the small-blocks the “W” series is huge. Depending on the intake manifold incorporated and which carburetor is used, the assembled engine has a dry weight of around 665 pounds (302 Kg).


A four-barrel carburetor mounted the “W” series engine from 1958 until ’61 and developed 250 hp (90 kW), which the company marketed as the Turbo-Thrust. The same time frame the Super Turbo-Thrust was available with Tri-Power, three two-barrel carburetors delivering 280 hp (210 kW). During this period, Chevrolet marketed the “W” series engine as the Special Turbo-Thrust with a larger four-barrel that produced 305 hp (227 kW).

Another higher powered configuration was available for the 1958-’60 model years. The Special Super Turbo-Thrust again is “Tri-Power” with 2×3 large carburetors giving 315 hp (235 kW). The ultimate horsepower rating for 1959 although it took third place in 1960 was the Special Turbo-Thrust version of the “W” series engine with Tri-Power gives up 320 hp (240 kW). For 1960, the next higher horsepower rating was a large four-barrel on the order sheet as a Special Turbo-Thrust engine producing 340 hp (250 kW). The most powerful engine to option for both 1960-’61 goes to the Special Super Turbo-Thrust with Tri-Power developing 350 hp (260 kW).

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