Chevrolet’s W-Series V-8 Details
In anticipation of larger size passenger cars and the need for a larger V-8 in their medium sized trucks, Chevrolet developed the W-Series “big-block” V-8. It was designed to develop more low end torque for these larger passenger cars and trucks. (To see the design and rational, see the SAE paper released by Chevrolet in 1958, HERE). The concept was that rather than just making a larger version of the small-block V-8, Chevrolet engineers were allowed a fee hand in design with the idea that they should make the engine as compact as possible and that it should be capable of displacement of at least 400 cubic inches. The result was the W-series big-block with its unusual cylinder head design that was directly related to the concept of a compact over-all size.
Thus, in 1958, Chevrolet released the first version of its new “Turbo-Thrust” engine, which measured 348 CID. The Turbo-Thrust had a bore and stroke of 4.125″ x3.25″, a definite an oversquare design. True to the request of management, the block itself wasn’t that much larger than the small-block – it was only” longer and 2.5″ wider. However, it was a large, heavy engine weighing about 120 pounds more. It had a forged-steel crankshaft, forged-steel connecting rods, and cast-aluminum pistons.
Offsetting the valves allowed the engine to be shortened in length.
The ability to compress the size without loosing appreciable valve-head size, was credited to the small-block’s stamped steel rocker arms allowing pedestals rather than a rocker shaft which would have put the valves in line and lengthened the engine. (see the image at left of why the heads had offset valves).
The arrow shows the combustion chamber inside the cylinder instead of in the head – which was flat.
Unlike previous Chevrolet OHV six and V-8 designs, the cylinder heads were flat – there was no combustion chamber. The chamber resided in the block. Thus, the the engine block deck surface was milled at a 74-degree angle instead of the usual 90-degree angle. The net result was that the combustion chamber was in the cylinder and would be shaped by the piston. An advantage of this type of design is that one cylinder head fits all, and combustion chamber design and compression ratio can be adjusted by changing piston top shape. (Coincidentally, Ford released a similar engine family in 1958, the “MEL” series with this type of cylinder head design, however it used a conventional rocker shaft and the engines were quire huge.
The base 348 CID engine was called “Turbo-Thrust” and was rated at 250 HP and was equipped with a single four-barrel carburetor and a hydraulic-lifter camshaft. One option was the “Super Turbo-Thrust. It was the same engine with three 2-barrel carburetors and rated at 280 HP. Next was the “Special Turbo-Thrust”, rated at 305 HP using a larger a single four-barrel carburetor. The top engine was the “Special Super Turbo-Thrust”. It received a mechanical-lifter camshaft and the three 2-barrel carburetor setup, for 315 HP.
All of these optional engines were carried over into 1959 and were joined by a 320 hp Special Turbo-Thrust (single four-barrel) and a 335 hp Special Super Turbo-Thrust (three 2-barrel carburetors). Up-rated 340 HP (single four-barrel) and 350 HP (three 2-barrel carburetors) versions were added for manual transmission cars in 1960. In the 348’s last year of passenger car production in 1961, the 315 and 320 HP versions were deleted from the option list.
The 409 CID engine replaced the 348 CID V-8 as Chevrolet’s top engine option in mid-1961. It was only available with a single four-barrel carburetor and was rated at 360 HP. In 1962, two versions of the 409 were released, a 380 HP single four-barrel and a 409 hp dual 4barrel setup. In 1963, the high point in the W-series engine family, was reached with 340, 400, and 425, HP versions of the engine were available. The limited production 1963 Z11 430 HP (under-rated) 427 CID version, was also available. (A “Mystery Engine” 427 block was also released with cylinder heads that would be emulated in the later Mark IV, but it was only run at Daytona and then withdrawn.)
All versions, except the Z11, were carried over into 1964. In its last year, 1965, the 409 CID 400 HP engine was available during the early part of the model year before it was replaced by the newer design Mark IV big blocks.
Neither the 348 nor 409 CID engine was used in Chevrolet light trucks, but the engine saw service in medium and heavy trucks.