Chevrolet Big-Block engine

The Chevrolet "Big Block" is a term for a series of large displacement V8 engines that have been developed and produced in the United States from the 1950s to the current day. As American automobiles grew in size and weight following the Second World War, the engines powering them had to keep pace. 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.

W-Series (Mark I)
The first version of the "Big Block" V8 Chevrolet engine, known as the W-series, was introduced in 1958. Chevrolet designed this engine for use in passenger cars and light trucks. This engine had an overhead valve design with offset valves and uniquely scalloped rocker covers, giving it a distinctive appearance. The W-series was produced from 1958 to 1965, and had three displacement options: The W-series engine was made of cast iron. The engine block had 4.84-inch (123 mm) 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. One minor difference between the 348 and 409/427 was the location of the engine oil dipstick: it was on the driver's side on the former and the passenger's side on the latter. No satisfactory explanation was ever offered for why this change was made. However, it did provide a fairly reliable way to differentiate between the smaller and larger versions of the engine.
 * 348 cubic inches (5.7 L), available from 1958 to 1961 in cars, and in light trucks through 1964;
 * 409 cubic inches (6.702 L), available from 1961 to 1965; and
 * 427 cubic inches (6.9973 L), available in 1962 and 1963.

As with the 265- and 283-cubic-inch "Small Block" engines, the W-series valve gear consisted of tubular steel push rods 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 USA 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 665 pounds (302 kg), depending on the type of intake manifold and carburetion systems present.

348
The first iteration of the W-series engine was the 1958 "Turbo-Thrust" 348-cubic-inch (5.7 L), originally intended for use in Chevrolet trucks but also introduced in the larger, heavier 1958 passenger car line. Bore was 4.125 in (104.8 mm) and stroke was 3.25 in (82.6 mm), resulting in a substantially oversquare design. This engine was superseded by the 409-cubic-inch 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 250 hp (186 kW). A special "Tri-Power" triple-two-barrel version, called the "Super Turbo-Thrust", produced 280 hp (209 kW). A "Special Turbo-Thrust" further upped the power output to 305 hp (227 kW) with a single large four-barrel carburetor. Mechanical lifters and triple two-barrel carburetors brought the "Special Super Turbo-Thrust" up to 315 hp (235 kW). For 1959 and 1960, high-output versions of the top two engines were produced with 320 hp (239 kW) and 335 hp (250 kW) respectively. In 1961, power was again increased to 340 hp (254 kW) for the single four-barrel model, and 350 hp (261 kW) when equipped with triple two-barrels.

409
A 409-cubic-inch (6.7 L) version was Chevrolet's top regular production engine from 1961 to 1965, with a choice of single or dual four-barrel carburetors. Bore and stroke were both up from the 348 to 4.312 in (109.5 mm) by 3.50 in (88.9 mm). On December 17, 1960, the 409 engine was announced along with the Impala SS (Super Sport) model. The initial version of the engine produced 360 hp (268 kW), with a single four-barrel Carter AFB carburetor. The same engine was upped to 380 hp (283 kW) in 1962. A 409 hp (305 kW) version of this engine was also available, developing 1 hp per cubic inch with a dual four-barrel aluminum intake manifold and two 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 425 hp (317 kW) at 6200 rpm with the 2X4 setup, 11.25:1 compression and a solid lifter camshaft. The engine was available through mid-1965, when it was replaced by the 396-cubic-inch 375 hp (280 kW) Mark IV big-block engine. In addition, a 340 hp (254 kW) version of the 409 engine was available from 1963–1965, with a single four-barrel cast-iron intake mounting a Rochester 4GC square-bore carburetor, and a hydraulic-lifter camshaft.

427 (Z11)
A special 427-cubic-inch (7.0 L) version of the 409 engine was used in the 1963 Chevrolet Impala Sport Coupe, 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 427 cubic inch engine with aluminum body parts, and a cowl-induction air intake system. 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 3.65 in (93 mm) 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 430 hp (320 kW) and 575 lb⋅ft (780 N⋅m). 50 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. Unfortunately, there is no evidence from GM that shows 57 cars were built.

Mark II
The so-called 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 409 cubic inches (6.7 L) version (Mark II) and ended with a 396 cubic inches (6.5 L) variant; however only the 427 cubic inches (7.0 L) engine (Mark IIS) was ever raced. It gained its nickname due to the incredible 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, then in Chevrolet's 1963 Daytona 500record-setting stock cars. 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
Packard V-8 tooling and production rights were considered for purchase by Chevrolet. Project did not proceed.

Mark IV
The Mark IV differed from the W-series engine in the placement of the valves and the shape of the combustion chambers. Gone was the chamber-in-block design of the W-series engine (which caused the power curve to drastically dip above 6500 RPM), and in its place was 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 ZL-1 Can-Am model), the "rat motor", as it was later nicknamed (small-block engine being a "mouse motor"), was slightly heavier than the W-series model, with a dry weight of about 685 pounds (311 kg). 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 pitch (bore spacing) of 4.84" with a larger 2.75" main bearing dimension, increased from the 2.50" of the older engine (in fact, the shorter-stroke 348 and 409 crankshafts could be installed with the use of "spacer bearings" without modifying the crankshaft). 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.

Also retained from the W-series design were the race-proven Moraine M400 aluminum bearings first used in the 409, as well as the highly efficient "side oiling" lubrication system, which assured maximum oil flow to the main and connecting rod bearings at all times. Later blocks intended for performance use had the main oil gallery moved up to the cam bearing bore area and provided "priority main" oiling, improving the oil system even further. These features, along with the robust crankcase design, sturdy forged steel crankshaft and massive four-bolt main bearing caps used in the high performance versions, resulted in what many have considered to be the most rugged and reliable large displacement automotive V8 engine design of all time.

366
The 366 Big Block V-8 (6.0 L) gasoline engine was used only in Chevrolet medium duty trucks and in school buses. It had a bore of 3.935" (99.95mm) and a stroke of 3.760" (95.5mm). This engine was made from the 1960s until the mid-1990s. The 366 used 4 rings on the pistons, as it was designed from the very beginning as a truck engine. The 366 was produced only as a tall-deck engine, with a deck 0.400" taller than the 396, 402, and 454 short-deck Big Blocks.

396 and 402
The 396-cubic-inch (6.5 L) V8 was introduced in the 1965 Corvette as the L78 option and in the Z16 Chevelle as the L37 option. It had a bore of 4.094 in (104.0 mm) and a stroke of 3.760 in (95.5 mm),[8][9] and produced 375 hp (280 kW) and 410 lb⋅ft (560 N⋅m). The solid lifter version was capable of being operated in the upper 6000 rpm range, and when installed in the 1965 Corvette, was factory-rated at 425 horsepower.

Introduced in 1970, the 402-cubic-inch (6.6 L) was a 396-cubic-inch bored out by 0.030 in (0.76 mm). Despite the fact that it was 6 cubic inches (98 cc) larger, Chevrolet continued marketing it under the popular "396" label in the smaller cars while at the same time labeling it "Turbo-Jet 400" in the full-size cars.

Power rating(s) by year: Used in: 396 and 402 Production codes
 * 1965: 375 hp (280 kW)/425 hp (317 kW)
 * 1966: 325 hp (242 kW)/350 hp (260 kW)/360 hp (270 kW)/375 hp (280 kW)
 * 1967: 325 hp (242 kW)/350 hp (260 kW)/375 hp (280 kW)
 * 1968: 325 hp (242 kW)/350 hp (260 kW)/375 hp (280 kW)
 * 1969: 265 hp (198 kW)(2bbl)/325 hp (242 kW)/350 hp (260 kW)/375 hp (280 kW)
 * 1970: 330 hp (250 kW)/350 hp (260 kW)/375 hp (280 kW)
 * 1971: 300 hp (220 kW) SAE gross; SAE net hp was 260 for dual exhaust and 206 for single exhaust
 * 1972: 240 hp (180 kW) SAE net for dual exhaust and 210 hp SAE net for single exhaust
 * 1965 Chevrolet Corvette
 * 1965–1972 Chevrolet Chevelle
 * 1967–1972 Chevrolet Camaro
 * 1968–1970 Chevrolet Nova
 * 1970–1972 Chevrolet Monte Carlo, Chevrolet trucks
 * 1965–1972 Chevrolet Biscayne, Chevrolet Bel Air, Chevrolet Impala, Chevrolet Impala SS, Chevrolet Caprice
 * 396


 * L-34: produced 1966-9, 10.25:1 compression, Holley (Q-jet 1968-9) carburetor, hydraulic lifters, oval port closed chamber heads, forged steel crankshaft, and two-bolt main caps. It produced 350 to 360 hp (260 to 270 kW).
 * L-35: produced 1965-9, had 10.25:1 compression, Q-jet carburetor, forged steel (1965-7) or nodular iron (1968-9) crankshaft, hydraulic lifters, oval port closed chamber heads, and two-bolt main caps. It produced 325 hp (242 kW).
 * L-37: similar to L-78 except for having hydraulic lifters and slightly milder cam; 2-bolt main caps; designed specifically for the 1965 Z16 Chevelle
 * L-66: produced 1969, rare two-barrel carburetor, 9:1 compression, nodular iron crankshaft, hydraulic lifters, oval port closed chamber heads, and two-bolt main caps. It produced 265 hp (198 kW).
 * L-78: produced 1965-9, had 800 cfm Holley carburetor, 11:1 compression, forged pop-top pistons, aluminum high-rise intake manifold, steel crankshaft, solid lifter cam (same as the L-72), rectangular ("square") port closed chamber heads, and four-bolt main caps. It produced 375 hp (280 kW) in mid-size cars, 425 hp (317 kW) in Corvettes.
 * 402


 * LS-3: produced 1970-2, 10.25:1 (1970) or 8.5:1 (1971) compression, hydraulic lifters, nodular iron crankshaft, and two-bolt main caps. It produced 330 hp (250 kW) (1970), 300 hp (220 kW) (1971), 210 or 240 hp (160 or 180 kW) (1972 net horsepower, single or dual exhaust).
 * L-34: produced 1970. Same as 396 ci L-34.
 * L-78: produced 1970. Same as 396 ci.