“W” Block 348 – 409 Chevy

As the 1950s began, the majority of automobiles had engines displacing less than 200 cubic inches, a milestone that had taken 50 years to achieve. By the decade’s end, the largest engines had doubled in size to more than 400 ci.

Even law enforcement had to catch up with such quick progress, as illustrated by Chevrolet’s promotion of the 1959 Chevy Biscayne police model. It was capable of 135 mph when equipped with Chevrolet’s “specially tuned, police-exclusive 348-ci V-8 engine.”

Around 50 years ago, the W engine was a brand-new piece of machinery rolling off the assembly line. Technicians assemble the 409 around 1963. Take note of how cleanly the components, such as pistons, were lined out for assembly. Additionally, take note of the heavy-duty engine stands.

Similarly, Chevy’s only single carburetor option for the new 348s was a four-barrel. Single and two-barrel applications were phased out, and you would never see them on a 348 or 409. It was a clever and necessary idea. The four-barrel on the larger engine produced significantly more power and helped the everyday car function more smoothly by operating at lower RPM and torque peak.


Three distinct components contributed to the development of the Chevrolet W series engines. Stock car and drag racing were instrumental in the development of the American V-8 engine, and its design and construction impacted the W engine. The third factor was the ever-increasing demand for newer, bigger, and better automobiles and engines by the car-buying public. Chevro-let’s-say-W engines evolved as a result of the convergence of these three variables.

With size, power, and potential growth as common denominators, Chevrolet developed a set of objectives for a new engine shortly after introducing its first overhead valve V-8, dubbed the small-block Chevy. It had to be larger in terms of power and displacement, but it also had to have room to become much larger. This engine would also be used in trucks, and physical size was a consideration. A completely new design was developed for the big-block engine, which would be used in the rapidly rising market for larger automobiles and trucks. As a result, a completely new design, the 348-ci engine, and the 348/408 family, were developed and introduced only three years after Chevrolet’s original V-8. As with the 265 and 283, the powerful 348/409 Chevys did not endure long, as development of the 396/427 Mark-IV big-block began concurrently.

General Motors kept the overall design of its vehicles consistent, which meant that the new big-block engines couldn’t physically exceed the small-block engines by much. The 348-ci displacement was chosen after it was recognized that prior configurations were too tiny. Chevrolet’s new W engine replaced an engine that was only 17 cubic inches smaller than the 300-inch early designs. When the “W” design was chosen, it was discovered to be quite similar in size to the small-block design. Indeed, it was only slightly wider and longer than the small-block, but gave a somewhat lower height, which could be advantageous for racers. However, appearances were misleading, as the engine reportedly weighed 140 pounds more than the small-block. When combined with the all-new X-shaped chassis, the combination forced racers to rethink their chassis settings and understand how they would perform on the race circuit.

Chevrolet’s first big-block engine included several unique features, including unusually curved valve covers. The use of staggered valves was one of the reasons for the altered shape, and the W engine received its moniker from this design element. Wedge-shaped combustion chambers were contained within the block, not in the heads, beneath those unusual heads. As a result, the pistons featured an unusual half-dome shape that allowed for the combustion chambers to be accommodated. Improved cooling flow directed its attention away from the exhaust valves and toward the source of the most heat generated in the heads. Indeed, the W possessed more odd characteristics than ordinary ones.

The first 348s were introduced in 1958 as Turbo-Thrust models, delivering 250 horsepower with a single four-barrel carburetor. A factory-installed three-barrel carburetor induction system increased horsepower by 30. From there, the 348 was fairly similar to many other engines of the era and offered greater power combinations.

In 1959, another 35 hp was added to the engine, bringing it to 315 hp, and in 1960, buyers could choose between a 335-hp and a 315-hp version. With 350 horsepower available in the final year of the 348, it broke the vaunted “one horse per cubic inch” barrier. Racers immediately discovered that installing dual quads increased that version’s horsepower to 355. A solid-lifter camshaft and a compression ratio of 11.25:1 aided in achieving that horsepower. Owners regarded the 348 as a very reliable engine, but the 409 did not share that reputation.

When the 409 was launched, it was believed to be a 348 that had undergone bore and stroke work. While technically correct, the transition from the 348 to the 409 was more involved than a reworked crankshaft and larger pistons. Although it appeared identical on the outside, the 409 was actually a new 348. The 348’s thin cylinder walls could not handle the bore size increase to 4.3125 inches, necessitating the block’s recasting. The 409 retained many of the attributes of the 348 but utilized more race-oriented components, such as the heads. While they retain their 409 identity, they will fit a 348 block if the matching 409 intake is utilized. One of the significant variations was in the heads, with the 409 models featuring larger pushrod holes and valve spring seats.

The first 409s were equipped from the factory with a solid-lifter cam, 17.5:1 rockers, and a large-bore Carter 4-barrel carburetor mounted on an aluminum intake that produced the same output as a 348 equipped with three 2-barrel carburetors. It wasn’t long before the 409, a seemingly magical number from the outset, began to appear on the nation’s drag strips and stock car racetrack. With racers utilizing the new engine, speed secrets developed and the engine swiftly progressed.

The Beach Boys’ song 409 popularized the 409 in the mid-1960s. Perhaps the 409 is the only engine to have a song dedicated to its exploits.

Any issues with the 409’s design evolution were swiftly and efficiently resolved. Enhancements included strengthening specific parts of the block and heads. Within three years, the 409 had evolved significantly from the initial models, which were little more than a progressed 348.


The 409 distinguished itself from the 348 in three important ways. It had the now-rare twin-snorkel air cleaner, with each intake tube angled forward 45 degrees from the engine’s centerline. The color of the valve covers was another point of differentiation. If the stamped-steel factory covers were silver, your engine was a 409- or 425-hp HO. The position of the oil dipstick was another quick and easy way to identify the new engine. The dipstick was relocated to the passenger side of the block on the new 409s.


The 348, the first W engine, is depicted in all its grandeur in a technical graphic. Chevrolet utilized this picture to demonstrate the vehicle’s distinction from the preceding small-block Chevy. This front-on view demonstrates the block’s deck’s substantially changed angle and its relationship to the cylinders and pistons.


The Z11 427 is the king of all W engines, having ruled the drag strips and contributing to the history of Chevrolet racing. Non-production components included a 3.65-inch forged steel crankshaft, forged pistons, aluminum large port heads, two-piece aluminum intake, aluminum water pump, custom Z11 damper, and factory-developed steel headers. A high-performance street 409 produced 360 horsepower; the Z11 produced 565 horsepower.


One of the earliest 409s constructed is on display in the showroom of W-engine guru Lamar Walden. Chevrolet made significant changes to these engines only months after they were released, making locating and restoring an original difficult. All of the changes were beneficial, as the engine became legendary.


The casing date is located on the block’s top surface on the driver’s side. Due of its rather horizontal surface, it is prone to becoming covered in dirt and filth. A wire bush should be able to clean it sufficiently for the date code to be read.


On store floors and race circuits across the country, the W engine made history. This breed’s initial 409 is distinguished by a Carter four-barrel carburetor and scalloped heads.


The exhaust manifold and side of the engine are shown in detail, together with the lengthy oil filter, oil pressure transmitting unit, and generator used in 1962. Although the new engine was larger and more powerful, it was not without problems, and Chevrolet overhauled it within months of its initial debut.

The top-of-the-line 409 vehicles had dual quad carburetors mounted on an aluminum high-rise intake on the outside and domed pistons, as well as a high-output oil pump, thicker pushrods, forged rods, and an improved camshaft installed within the block. Increased porting and stronger valvesprings were used to strengthen the heads. Compression ratios were an astonishing 11:1, with the top 409 vehicles producing an incredible 425 horsepower through 1964. 409 machines frequently turned 14-second times at the drag strip straight off the showroom floor with little race tuning.

The original 409 was powered by a single RPO580 engine producing 360 horsepower at 5,800 rpm and 409 ft-lbs of torque. Chevrolet advertising made it quite obvious that this was a force to be reckoned with, with a torque figure that matched the engine size.

The following year, two 409s (RPO580 and RPO587) offered a minor compression drop (.25), but increased horsepower to 380 and 409, respectively. Chevrolet’s advertising department finally had a horsepower figure that matched the cubic inches, and it was far over 400. The RPO580 had a single four-barrel carburetor, whereas the RPO587 had two four-barrel carburetors. Both engines produced the same amount of torque, 420 ft-lbs.

Chevrolet renamed the 409 in 1963, renaming it the L33, L31, and L80 with 340, 400, and 425 horsepower, respectively. The L80 was the only 409 equipped with two four-barrel carburetors. The L31 and L80 had 425 ft-lbs of torque, whereas the L33 had 420 ft-lbs. In 1964, the same three 409s with identical horsepower ratings were introduced. It was the final year that the L80 was available with two four-barrel carburetors. The 409 was discontinued in 1965, with only two models available: the L33 (340 hp) and the L31 (400 hp).

After 1963, the 409’s option count and growth slowed for two reasons. General Motors ceased sponsorship for official factory racing and its underground or back-door activities, most likely as a result of the government’s investigation into alleged antitrust crimes at GM. Another reason was that the cubic inch wars were in full swing, and Chevrolet was already developing the engine to replace the W series.