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In 1958, Chevrolet released what is reputedly, their first version of the big-block V8, the 348 cubic-inch engine. Referred to as the W-series because of the shape of the cylinder head, this engine was designed for use in passenger cars and light trucks. The overhead valve design utilized an offset valve positioning and easily recognizable valve covers — it definitely had a look of its own.
The cast-iron engine had 4.84-inch bore centers, two-bolt main bearing caps, and a “side oiling” lubrication system, as the main oil gallery was located low on the driver’s side of the engine.
A small difference between the 348 cubic-inch and the later 409 cubic-inch engines that many people miss, was the location of the dipstick. On the 348 ci engines, it was on the driver’s side of the engine, and the 409 ci engine had it located on the passenger’s side.
The cylinder heads on the W-series engine were machined flat, and therefore did not have a conventional combustion chamber. Instead, the engine uses a combustion chamber design that is not incorporated into the cylinder head. When looking at the cylinder head, you will notice there is a small relief area cut around the valves.
The valves in the cylinder heads didn’t seat flush against the valve seat. The outer edges of the valves would hang over the outside the valve seats. That valve’s face also protruded from the seat and past the deck of the head’s surface.
As the piston reached top-dead-center, the unusual angle of the piston’s crown combined with the angled cylinder-head deck, formed a wedge-shaped combustion chamber area with a pronounced quench area. This arrangement resulted in an engine that developed a broad torque curve.
The Turbo-Thrust 348-cubic-inch engine had 4.125-inch cylinder bores, and a stroke of 3.25 inches. With a four-barrel carburetor, the Turbo-Thrust produced 250 horsepower. The Tri-power version, called the Super Turbo-Thrust, developed 280 horsepower. If that wasn’t enough, a Special Turbo-Thrust option with a larger four-barrel carburetor upped power to 305 horsepower. Shooting for the moon got the buyer a Special Super Turbo Thrust engine with mechanical lifters and three two-barrel carburetors.
A 1961 348 cubic-inch engine with three two-barrel carburetors.
This upgrade increased output to 315 horsepower. In 1959 and 1960, higher-output renditions of the top-two power producing versions were offered that developed 320 and 335 horsepower. In 1961, horsepower was again increased to 340 in single-four-barrel engines, and 350 if equipped with three two-barrels.
