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Chevrolet Big-Block Engine

The Chevrolet big block is a series of large displacement V8 engines that were developed in the USA during the 1950s and 1960s. As American automobiles grew in size and weight following the Second World War the engines powering them had to keep pace. Chevrolet had introduced their popular small block V8 in 1955 but needed something larger to power their medium duty trucks and the heavier cars that were on the drawing board. The decision was made by Chevrolet to develop an all-new design for large-displacement use. This engine family had two generations, the "W" series, and the Mark IV series.

Generation 1: "W" Series

Generation 1: "W" Series

The first ever production big block V8 Chevrolet engine was the "W" series, released in 1958 for passenger car and truck use. This engine was an overhead valve design, with offset valves and unique scalloped rocker covers, giving it a distinctive appearance. The "W" series was produced from 1958 to 1965, with three displacements offered: 348 cubic inches (5.7 L), available from 1958 to 1961 in cars and through 1964 in trucks; 409 cubic inches (6.7 L), available from 1961 to 1965; and 427 cubic inches (7.0 L), available only in 1963.

As was the norm at the time, the "W" engine was of cast iron construction. The block had 4.84-inch (123 mm) bore centers, two-bolt main bearing caps, a "side oiling" lubrication system (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 passenger's side on the latter. No satisfactory explanation was ever presented for why this seemingly useless change was made. However, it was a fairly reliable way to differentiate between the smaller and larger versions of the engine.

As with the 265 and 283 cubic inch small block engines, the "W" engine valve gear consisted of tubular steel push rods operating stud-mounted, stamped steel rocker arms. The push rods also acted as a conduit for oil flow to the valve gear. Due to the relatively low mass of the valve train, mechanical lifter versions of the "W" engine were capable of operating at speeds well beyond 6000 RPM.

Unlike many of its contemporaries, the "W" combustion chamber was in the upper part of the cylinder, not the head, the latter which only had tiny recesses for the valves. This arrangement was achieved by combining the use of a cylinder head deck that was not perpendicular to the bore with a crowned piston, 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 plug protruded vertically into this chamber, which tended to cause a rapidly moving flame front during combustion.

The theory behind this sort of arrangement is that maximum brake mean effective pressure 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 trucks and the heavier cars that were in vogue in the USA at the time of the engine's development.

The "W" had a dry weight of approximately 665 pounds (302 kg), depending on intake manifold and carburetion, and was a physically massive engine compared to its small block predecessor.



The first iteration of the "W" 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 (82.5 mm), resulting in a substantially oversquare design. This engine was superseded by the 409 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" upped the output to 305 hp (227 kW) with a single large four-barrel. Mechanical lifters and the three 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 (253 kW) for the single four-barrel model, and 350 hp (261 kW) when equipped with three two-barrels.



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 at 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 horsepower (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. 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. This engine was immortalized in the Beach Boys song titled "409". The engine was available through mid 1965 when it was replaced by the 396-cubic-inch 425 hp (317 kW) Mark IV big-block engine. In addition, a 340 hp (253 kW) version of the 409 engine was available from 1963–1965, with a single-four-barrel cast-iron intake mounting a Rochester 4GC carburetor, and a hydraulic-lifter camshaft.

427 (Z11)

427 (Z11)

A special 427 cubic inches (7.00 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, including aluminum engine and body parts and a cowl-induction air intake system, along with the 427 engine. The aluminum body parts were fabricated in Flint, MI 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 (92.7 mm) stroke. A high-rise two piece aluminum intake manifold and dual Carter AFB carbs fed a 13.5:1 compression ratio to produce an under-rated 430 hp (321 kW) and 435 ft·lbf (590 N·m). 50 RPO Z11 cars were produced at the Flint plant. GM Documents exist that 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. No evidence from GM has been found that show 57 cars were built.

Generation 2: Mark IV Series

Generation 2: Mark IV Series

Development of the second generation big-block started with the so-called Mystery Motor used in Chevrolet's 1963 Daytona 500 record-setting stock cars. This "secret" engine was a substantially modified form of the "W" engine, and was subsequently released for production use in mid-1965 as the Mark IV, referred to in sales literature as the "Turbo-Jet V8."

Where the Mark IV differed from the "W" engine was in the placement of the valves and the shape of the combustion chambers. Gone was the chamber-in-block design of the "W" (which caused the power curve to drastically sag 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" 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 the cylinder centerline, rather than the straight in relationship of the "W" 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" model 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 (the small-block engine being a "mouse motor"), was slightly heavier than the "W" model, with a dry weight of about 685 pounds (310.7 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 similarities with the "W" engine. The cylinder block, although more substantial in all respects, used the same cylinder bore centers and main bearing dimensions as the older engine (in fact, the shorter stroke 348 and 409 crankshafts could be installed without modification). 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" 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. 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.

396 and 402

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. It had a bore of 4.094 in and stroke of 3.76 in (104 mm by 96 mm), and produced 425 hp (317 kW) and 415 ft·lbf (563 N·m). This version of the 396 was equipped with four bolt main bearing caps and was very comfortable with being operated in the upper 6000 rpm range.

Introduced in 1970, the 402-cubic-inch (6.6 L) was a 396-cubic-inch bored out by 0.030 in (0.8 mm). Despite the fact that it was 6 cubic inches (98 cc) larger, Chevy continued marketing it under the popular "396" label in the smaller models, and as the "Turbo-Jet 400" in the full-size series.

Power rating(s) by year:

    * 1965: 375 hp (280 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)
    * 1972: 240 hp (180 kW)

Used in:

    * 1965 Chevrolet Corvette
    * 1965–1972 Chevrolet Chevelle
    * 1967–1972 Chevrolet Camaro
    * 1968–1970 Chevrolet Nova
    * 1970–1972 Chevrolet Monte Carlo
    * 1965–1972 Chevrolet Biscayne, Chevrolet Bel Air, Chevrolet Impala, Chevrolet Impala SS, Chevrolet Caprice



The highly successful and versatile 427 cubic inch (7.0 L) version of the Mark IV engine was introduced in 1966 as a production engine option for full sized Chevrolets and Corvettes. The bore was increased to 4.25 inches (108 mm), with power ratings varying widely depending on the application. There were smooth running versions with hydraulic lifters suitable for powering the family station wagon, as well as rough idling, high-revving solid lifter models that resembled racing powerplants.

Not every version of the 427 was available in every car, and ordering the highest performance versions often required that other options be added to or deleted from the car (for example, power steering wasn't available with the high performance models). This relationship between engine configuration and vehicle options often resulted in what was jokingly referred to as a "racing taxicab," the description usually applied to a minimally equipped, plain looking, two door Biscayne sedan fitted with the 425 horsepower (317 kW) version of the 427— (RPO L72), resulting in a vehicle whose performance was the polar opposite of a taxi. This lightweight, big-block Biscayne was also commonly referred to as "Bisquick."

Perhaps the ultimate 427 for street applications was the 435 horsepower (324 kW) L71 version available in 1967 to 1969 Corvettes, and in the Italian Iso Grifo. This engine was identical to the 425 hp (317 kW) L72 427 (first introduced in 1966) but was fitted with three two barrel carburetors in lieu of the L72's single 4 barrel. Both engines utilized the same high lift, long duration, high overlap camshaft and large port, cast iron heads in order to maximum cylinder head flow (and, hence, engine power) at elevated engine operating speeds. Consequently, the engines offered very similar performance and resulted in a car whose performance was described by one automotive journalist as "the ultimate in sheer neck-snapping overkill." Typical magazine road tests of the day yielded sub-6 second zero to 60 miles per hour (97 km/h) times and quarter miles in the mid 13 second/106 MPH range for both the L72 and L71.

RPO L89 was an L71 fitted with aluminum heads (often dealer installed). While this option produced no power advantage, it did reduce engine (and hence, vehicle) weight by roughly 75 pounds (34 kg). This resulted in superior vehicle weight distribution for improved handling, although any difference in straight line performance was essentially negligible.

The most legendary version of the 427 was undoubtedly the 1969 ZL1 engine. It was developed primarily for Can-Am racing, where it was very successful in cars like the Chaparrel 2F and McLaren M8B. The ZL1 had specifications nearly identical to the production L88 version of the 427, but featured an all-aluminum cylinder block in addition to aluminum cylinder heads, which dropped total engine weight into small block Chevy territory (approx. 575 lb/261 kg dressed). The engine was also fitted with the new open combustion chamber cylinder heads, a light weight aluminum water pump, a camshaft that was slightly "hotter" than the L88's and a specially tuned aluminum intake manifold. Like the L88, the ZL1 required 103 octane RON (minimum) fuel, which made both engines largely unsuitable for street use in an era where 102 octane RON (Sunoco 260) represented the highest octane gasoline sold at common retail stations. Impressive as the ZL1 was in its day and despite the "larger than life legends" surrounding it, actual engine dyno tests of a certified production line stock ZL1 revealed 376 SAE net HP, with output swelling to 524 Gross HP with the help of optimal carb. and ignition tuning, open long tube racing headers and with no power sapping engine accessories or air cleaner in place. ZL1 DYNO TEST - COPO CAMARO WEBSITE A second engine dyno test conducted on a second production line stock (but recently rebuilt and partially blueprinted) ZL1 revealed nearly identical figures for the various "Gross" conditions. 2nd ZL1 DYNO TEST Magazine tests of the ZL1 were quite rare due to the rarity of the engine itself. "High Performance Cars" tested a production line stock version and recorded a 13.1 second/110 MPH quarter mile, which correlates quite well with the previously referenced 376 Net HP figure. "Super Stock and Drag Racing Magazine" recorded an 11.62 second/122.15 MPH quarter mile in a ZL1 Camaro that was professionally tuned and driven by drag racing legend Dick Harrell, although that car was equipped with open long tube S&S equal length headers, drag slicks and minor suspension modifications. The 122.15 MPH trap speed indicated very low 11 second ET potential (e.g. with larger drag slicks) and suggested something on the order of 495 "as installed" HP in that modified configuration. This large difference in power suggests that the OEM exhaust manifolds and exhaust system were very restrictive in the ZL1 application, as was also the case with the similar L88.

The race-prepped ZL1s that were utilized in Can-Am racing were capable of developing something on the order of 600 "as raced" HP as the result of complete engine blueprinting, fuel injection, more aggressive cam-shaft grinds, custom fabricated, power optimizing long tube racing headers, dry sump lubrication and various other power and durability enhancing changes. It is this figure that is often erroneously cited as the "actual" output of production line stock ZL1 passenger car engines (e.g. 1969 COPO 9560 Camaro).

The 4718 dollar cost of the ZL1 option doubled the price of the 1969 Corvette, but resulted in a car with exceptional performance for its day. Just two production Corvettes (factory option at dealer) and 69 Camaros (non-dealer option from factory - COPO 9560) were built with the ZL1.

Chevrolet capitalized on the versatility of the 427 design by producing a wide variety of high performance, "over the counter" engine components (marketed as "heavy duty" or "extra capacity" components to mask their intended racing application), as well as ready-to-race "replacement" engines in shipping crates. Some of the components were developed to enhance the engine's reliability during high RPM operation, possibly justifying the use of the description "heavy duty." However, most of these items were racing parts originally designed for Can-Am competition that found their way on to dealers' shelves, and were meant to boost the engine's already impressive power output. As a result of this activity, the 427 quickly became dominant in drag racing.

Beginning in 1969, the highest performance 427 models were fitted with the new open (vs. closed) chamber cylinder heads, which, along with design improvements in crankshafts, connecting rods and pistons adopted from the Can-Am development program, resulted in an engine with substantially increased performance and reliability. This development culminated in a specialty version of the engine called the ZLX, which was essentially a ZL1 engine built with the L88 engine's sturdy, four bolt main bearing iron block (it has been suggested that "ZLX" was a code name for ZL1 crossover). The ZLX, available as a short block assembly or complete "replacement" engine in the crate from a few dealers, was a resounding success and became a best-seller by after market racing components standards—the closest thing to an all-out competition engine ever offered to the general public.

Chevrolet gave all 427 engines except the ZL1 a torque rating of 460 ft·lbf (624 N·m).


   1. ^ Chevrolet actually advertised this engine as 450 hp (336 kW) for a short period of time. There is speculation over whether this engine actually put out 450 Gross HP, or if this was a marketing oversight that was later corrected.
   2. ^ L88 had a 12.5:1 compression ratio with closed chamber heads except during the last half of 1969, when it had open chambered heads that yielded 12.0:1
   3. ^ L88 was rated for 430 hp (320 kW) at 5200 rpm. With stock exhaust manifolds and operation in the 6,800 rpm range, it was generally accepted that the engine was capable of producing in excess of 500 Gross HP with free-flowing (open) long tube headers.

    * 1966–1969 Chevrolet Biscayne
    * 1966–1969 Chevrolet Caprice
    * 1966–1969 Chevrolet Impala
    * 1966–1969 Chevrolet Corvette
    * 1968–1969 Chevrolet Camaro (most were dealer installed, but in 1969 both the L-72 and the ZL-1 were factory options)



The big-block was expanded again for 1970 to 454 cubic inches (7.4 L) with a 4.251 in (108 mm) bore and 4 in (102 mm) stroke. The 1970 Chevy Corvette LS5 version of this engine produced 390 hp (291 kW) and 500 ft·lbf (678 N·m), and the LS6 engine was rated at 450 hp (336 kW). It has been suggested that the LS6 was substantially underrated and actually produced well over 500 horsepower (370 kW) as delivered from the factory, although there is no empirical evidence to support this claim. Indeed, the AHRA ASA Class record holding Chevelle LS6 for the 1970 season posted a record setting trap speed of 106.76 mph (171.81 km/h) "1970 ASA LS6 454 Records", which suggests something on the order of 370 "as installed" (SAE Net) HP for a 3,900 pounds (1,800 kg) car and driver combination.

A 465 hp (347 kW) and 490 lb·ft (664 N·m) version of the 454, dubbed LS7 was also designed but never went to production. However, a handful of LS7 intake manifolds were produced and sold by a handful of Chevy dealers as performance parts. The LS7 was later offered as a crate engine from GM and advertised at 500 hp (370 kW).

Power began falling off after 1970, with the 1971 LS5 producing 365 hp (272 kW) and 465 lb·ft (630 N·m), and the LS6 option coming in at 425 hp (317 kW) and 475 lb·ft (644 N·m). Only the LS5 remained in 1972, when SAE net power ratings and the move towards emission compliance resulted in to 270 hp (201 kW) and 390 lb·ft (529 N·m). The 1973 LS4 produced 275 hp (205 kW) and 390 lb·ft (529 N·m), with 5 hp (4 kW) and 10 lb·ft (14 N·m) gone the following year. Hardened valve seats helped allow these engines to last much longer than the earlier versions, even without the protection previously provided by lead from fuel. 1974 was the last year of the 454 in the Corvette though the Chevelle offered it in the first 1/2 of the 1975 model year. It was also available in the full size Impala/Caprice until model year 1976.

GM continued to use the 7.4 L (454 cu in) in their truck line, introducing a new Vortec 7400 version in 1996. GM also introduced the 7.4 L 454 EFI in 1990 (known as the GEN V; the previous generation was known as the Mark IV produced between 1965-90; the GEN prefix was used since Ford Motor Company owns the Mark V naming rights since it was used on a Lincoln automobile between 1977-79), which was electronically fuel injected giving more power and torque. Instead of the regular 290 hp (220 kW), the 454 EFI version cranked out 365 hp (272 kW) and 415 lb·ft (563 N·m) of torque. The 454 EFI power ratings were very similar to the early 1970s LS5 454, which was found in early 1970s corvettes and chevelles. The 7.4 L 454 EFI was found on GM 3500 trucks throughout the early 1990s until replaced with the Vortec 7400 (GEN VI) in 1996.

    * 1970–1976 Chevrolet Cars
    * 1970–1974 Chevrolet Corvette



The 502-cubic-inch (8.2 L) was offered in various fleet and service vehicles in the late 80's and early 90's. It had a bore of 4.466 with a stroke of 4.00 and was a cast iron 4-bolt main block. Later GM offered it in their Performance Parts catalog, available as multiple crate motors with horse power ratings between 338 hp (252 kW) to 502 hp (374 kW), and torque of 470 lb·ft (637 N·m) to 567 lb·ft (769 N·m) in "Base" and "Deluxe" packages. The "Ram Jet 502" (502 hp (374 kW) / 565 lb·ft (766 N·m)) crate motor was offered with fuel injection, and came as a turn key setup which includes all the wiring and electronics needed to operate in any vehicle.



Chevrolet began offering a 572-cubic-inch (9.4 L) "crate motor" in 2003 which produced 720 hp (537 kW) and 685 lb·ft (929 N·m) of torque, and more recently a 620 hp (462 kW) / 650 lb·ft (881 N·m) version capable of running on 93 octane street gasoline.
Source: Wikipedia

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