The Chevrolet big-block engine is a series of large-displacement, naturally-aspirated, 90°, overhead valve, gasoline-powered, V8 engines that was developed and have been produced by the Chevrolet Division of General Motors from the late 1950s until present. They have powered countless General Motors products, not just Chevrolets, and have been used in a variety of cars from other manufacturers as well - from boats to motorhomes to armored vehicles.
Chevrolet had introduced its popular small-block V8 in 1955, but needed something larger to power its medium duty trucks and the heavier cars that were on the drawing board. The big-block, which debuted in 1958 at , was built in standard displacements up to , with aftermarket crate engines sold by Chevrolet exceeding .
Mark I (W-series) The first version of the "big-block" V8 Chevrolet engine, known as the W-series, was introduced in 1958. Designed for use in passenger cars and light trucks, the cast iron block, overhead valve engine had offset valves and uniquely scalloped valve covers, giving it a distinctive appearance.
The W-series was produced from 1958 to 1965, in three displacements: , available from 1958 to 1961 in cars, and in light trucks through 1964; , available from 1961 to 1965; and , available in 1962 and 1963.
The engine had 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 – but for the location of the engine oil dipstick, on the driver's side on the 348 and the passenger's on the 409/427. No satisfactory explanation was ever offered for why this change was made, but it did provide a reliable means of distinguishing a 348 from the larger engines.
As with the "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 US 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 , depending on the type of intake manifold and carburetion systems present. It was 1.5 inches longer, 2.6 inches wider, and 0.84 inches shorter than the 283 "small-block"."Engineering the 'W' Engine – Chevrolet's 348-cu-in. V8." SAE Transactions, Volume 67 (1959), 103.
General Motors engineers explained, in 1959, reasons behind the combustion-in-block setup. Anticipating varied future compression ratios in future auto and truck use: "It was obvious that with the combustion chamber placed within the cylinder head, the foundry must retool every time a compression change is in order. The necessity of making special heads to provide a range of compression ratios and to permit attachment of accessory mountings for the various model applications is of serious concern to the manufacturing and service departments ... Inclining the top of the block to 16° and shaping the top of the piston like a gabled roof with a 16° angle resulted in a 32° wedge-shaped combustion space ... The addition of two milled cutouts [in the head] to extend the volume of the combustion wedge can create a compression ratio of 7.5:1; one milled cutout produces a 9.5:1 compression ratio. The difference between the volume of these cutouts provides a wide compression range without making any changes in the piston or cylinder head. The number or size of cutouts is varied simply by adding or removing cutters.""Engineering the 'W' Engine – Chevrolet's 348-cu-in. V8." SAE Transactions, Volume 67 (1959), 104–105.
348 The first iteration of the W-series engine was the 1958 "Turbo-Thrust" , originally intended for use in Chevrolet trucks but also introduced in the larger, heavier 1958 passenger car line. Bore and stroke was , resulting in a substantially oversquare design. This engine was superseded by the 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 . A special "Tri power" triple-two-barrel version, called the "Super Turbo-Thrust", produced . A "Special Turbo-Thrust" upped the power output to with a single large four-barrel carburetor. Mechanical lifters and Tri power brought the "Special Super Turbo-Thrust" up to . For 1959 and 1960, high-output versions of the top two engines were produced with and respectively. In 1961, power was again increased to for the single four-barrel model, and when equipped with Tri power.
+VersionsFirst YearLast YearModel NameFeaturesPower (Advertised Gross)19581961Turbo-Thrust4 barrelSuper Turbo-Thrust 3x2 barrelSpecial Turbo-Thrust4 barrel1960Special Super Turbo-Thrust 3x2 barrel1959Special Turbo-Thrust4 barrel1961Special Super Turbo-Thrust 3x2 barrel1960Special Turbo-Thrust4 barrelSpecial Super Turbo-Thrust 3x2 barrel
409
A version was Chevrolet's top regular production engine from 1961 to 1965, with a choice of single or 2X4-barrel Rochester carburetors. Bore x stroke were both up from the to . On December 17, 1960, the 409 engine was announced along with the Impala SS (Super Sport) model. The initial version of the engine produced with a single 4-barrel Carter AFB carburetor. The same engine was upped to in 1962. A version of this engine was also available, developing 1 hp per cubic inch with a dual-snorkel intake manifold and dual aluminum four-barrel Carter AFB carburetors. It had a forged steel crankshaft. This dual-quad version was immortalized in the Beach Boys song titled "409".
In the 1963 model year, output reached at 6000 rpm and at 4200 rpm of torque with the Rochester 2X4-barrel carburetor setup, a compression ratio of 11:1 and solid lifters. The engine was available through mid-1965, when it was replaced by the Mark IV big-block engine. In addition, a version of the 409 engine was available from 1963 to 1965, with a single 4-barrel cast iron intake mounting a Rochester 4GC square-bore carburetor, and hydraulic lifters.
427 (Z11) A special version of the 409 engine was used in the 1963 Impala Sport Coupé, ordered under Chevrolet Regular Production Option (RPO) Z11. This was a special package created for drag racers, as well as NASCAR, and it consisted of a cowl-induction engine and body with selected aluminum stampings. The aluminum body parts were fabricated in Flint, Michigan at the facility now known as GM Flint Metal Center. Unlike the later, second-generation 427, it was based on the W-series 409 engine, but with a longer stroke. A high-rise, two-piece aluminum intake manifold and dual Carter AFB carburetors fed a 13.5:1 compression ratio to produce an under-rated SAE gross and . Fifty RPO Z11 cars were produced at the Flint GM plant.
Extant GM Documents show 50 Z11 engines were built at the GM Tonawanda Engine plant for auto production, and 20 partial engines were made for replacement/over-the-counter use. There is no evidence from GM that shows 57 cars were built.
Mark II The "Mystery Motor", known internally as the Mark II or Mark IIS, is a race-only engine produced for the 1963 season. Development began with a version (Mark II) and ended with a variant; however only the engine (Mark IIS) was ever raced. It gained its nickname due to the speeds cars equipped with it attained during its debut, being considerably faster than the well known W-series powered cars. The engine was first used in Mickey Thompson's Z-06 Corvettes at Daytona in the 1963 Daytona 250 Miles – American Challenge Cup, and then in 1963 Daytona 500 where the number 13 car, driven by Johnny Rutherford, finished four laps down (in ninth place), with the top five cars being the heavier 1963 Ford Galaxie 500's. This "secret" engine was a unique design incorporating aspects of both the W-series and the mid-1965 introduced Mark IV, referred to in sales literature as the "Turbo-Jet V8".
Mark III Richard Keinath, the original Mark II and IV design engineer stated that the MK III was a regular MK II design with a larger bore, but the Tonawanda plant didn't want to cast a block with a bore that large. The rumor that Packard's V8-engine tooling and production rights were considered for purchase by Chevrolet, was evidently true but never came to fruition.
The Mark III was supposed to be a Mark II with bigger bore centers, but it never left the drawing board due to high tooling costs.
Mark IV The Mark IV differed from the W-series engine in the placement of the valves and the shape of the combustion chambers. The chamber-in-block design of the W-series engine (which caused the power curve to drastically dip above 6500 rpm), was replaced by a more conventional wedge chamber in the cylinder head, which was now attached to a conventional 90 degree deck. The valves continued to use the displaced arrangement of the W-series engine, but were also inclined so that they would open away from the combustion chamber and cylinder walls, a design feature made possible by Chevrolet's stud mounted rocker arms. This alteration in valve placement resulted in a significant improvement in volumetric efficiency at high RPM and a substantial increase in power output at racing speeds. Owing to the appearance of the compound angularity of the valves, the automotive press dubbed the engine the "porcupine" design.
As part of the head redesign, the spark plugs were relocated so that they entered the combustion chamber at an angle relative to the cylinder centerline, rather than the straight-in relationship of the W-series engine. This too helped high RPM performance. Due to the new spark plug angle, the clearance provided by the distinctive scalloped valve covers of the W-series was no longer needed, and wide, rectangular covers were used.
In all forms (except the aluminum ZL-1), the Mark IV was slightly heavier than the W-series model, with a dry weight of about . Aside from the new cylinder head design and the reversion to a conventional 90 degree cylinder head deck angle, the Mark IV shared many dimensional and mechanical design features with the W-series engine. The cylinder block, although more substantial in all respects, used the same cylinder bore spacing of with a larger main bearing dimension, increased from the of the older engine. Like its predecessor, the Mark IV used crowned pistons, which were castings for conventional models and impact extruded (forged), solid skirt types in high performance applications.