Chevrolet Big-Block engine

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"Big block" is the term used to describe the large displacement V8 engines that were developed in the USA during the 1950's and 1960's. 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.

Contents

[edit] Generation 1: "W" Series

The ancestral engine of what is most often thought of as the Chevrolet big block was the "W" series V8, first 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, available from 1958 to 1961 in cars and through 1964 in trucks; 409 cubic inches, available from 1961 to 1965; and 427 cubic inches, 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 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. The valves used in the high performance models were larger than those of the standard units, but other than that, the heads were all alike. 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 the the relatively low mass of the valve train, mechanical lifter versions of the "W" engine was 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 lb (300 kg), depending on intake manifold and carburetion, and was a physically massive engine compared to its small block predecessor.

[edit] 348

The first iteration of the "W" engine was the 1958 "Turbo-Thrust" 348 in³ (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.

The base Turbo-Thrust, with a four-barrel carburetor, 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, horsepower 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.

Versions:

First
Year		 Last
Year		 Model Name Features Power
1958 1961 Turbo-Thrust 4 barrel 250 hp (186 kW)
1958 1961 Super Turbo-Thrust "Tri-Power" 3x2 barrel 280 hp (209 kW)
1958 1961 Special Turbo-Thrust 4 barrel 305 hp (227 kW)
1958 1960 Special Super Turbo-Thrust "Tri-Power" 3x2 barrel 315 hp (235 kW)
1959 1960 Special Turbo-Thrust 4 barrel 320 hp (239 kW)
1959 1961 Special Super Turbo-Thrust "Tri-Power" 3x2 barrel 335 hp (250 kW)
1960 1961 Special Turbo-Thrust 4 barrel 340 hp (253 kW)
1960 1961 Special Super Turbo-Thrust "Tri-Power" 3x2 barrel 350 hp (261 kW)

[edit] 409

A 409 in³ version was Chevrolet's top regular production engine from 1961 to 1964, with a choice of single- or dual-four-barrel carburetors. A 409 horsepower version of this model was released in 1962, developing 1 horsepower per cubic inch.

Output reached 425hp at 6200 RPM in '63 with the 2X4 setup. This included a solid lifter camshaft. Bore and stroke were both up from the 348 at 4.312 in (109.5 mm) by 3.50 in (88.9 mm). The engine was available through mid 1965. This engine was immortalized in the Beach Boys song titled "409".

[edit] 427 (Z11)

A special 427 in³ (7.0 L) version of the 409, called the Z11, was used in the 1963 Chevrolet Impala Sports Coupe. Unlike the later second generation 427, it was a basic W-Series 409 engine, but with a longer 3.65 in (92.7 mm) stroke. An 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). Only 50 Z11s were ever produced.

[edit] 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 high RPM volumetric efficiency and resulted in 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.

[edit] 396 and 402

The 396 in³ (6.5 L) V8 was introduced in the 1965 Corvette as the L78 option. It had larger bore and stroke at 4.094 in by 3.76 in (104 mm by 96 mm) than any previous small-block and produced an amazing 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 in³ was a 396 in³ bored out by .030 in (0.8 mm). Despite the fact that it was 6 c.i. 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.

[edit] 427

L36 427 in a 1966 Chevrolet Corvette
Enlarge
L36 427 in a 1966 Chevrolet Corvette
L89 427 in a 1967 Chevrolet Corvette
Enlarge
L89 427 in a 1967 Chevrolet Corvette

The highly successful and versatile 427 cubic inch (7 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, 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, producing well over 400 horsepower.

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 brutally powerful 425 horsepower version of the 427—a vehicle which more resembled a guided missile than a taxi.

Perhaps the ne plus ultra in 427 street applications was the L89 435 horsepower version available in 1967 to 1969 Corvettes. This engine was equipped with three two barrel carburetors and large port aluminum heads for maximum high RPM air flow, and resulted in a car whose performance was described by one automotive journalist as "the ultimate in sheer neck-snapping overkill." The "tri-power" 427 could accelerate the 1967 Corvette coupe from zero to 60 miles per hour in little more than four seconds and, when suitably tuned for drag racing, turn in 11 second, 125 mile per hour quarter mile performances, suggesting a true power output in the range of 550 horsepower.

The most famous version of the 427 was undoubtably the 1969 ZL1 engine. Developed for Can-Am racing, where it was very successful, the ZL1 had specifications nearly identical to the production L88 version of the 427, but had an all-aluminum cylinder block that weighed 100 lb less than a similar iron block. The engine was also fitted with the new open combustion chamber cylinder heads, a light weight aluminum water pump and a specially tuned aluminum intake manifold, resulting in an engine weighing little more than a small block, but capable of 600 plus horsepower in racing tune. The 4718 dollar cost of the ZL1 option doubled the price of the 1969 Corvette. Just two production Corvettes and 69 production Camaros were built with this option.

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 obvious racing parts originally designed for Can-Am competition that found their way on to dealers' shelves, and were meant to boost the engines already impressive power output. As a result of this activity, the 427 quickly became dominant in drag racing.

The version of the 427 produced from 1966 to 1969 was fitted with essentially the same cylinder heads as used with the 396, a type often referred to as the closed combustion chamber design. Starting in 1969, the highest performance models were fitted with the new open chamber cylinder head, which along with design improvements in crankshafts, connecting rods and pistons adopted from the Can-Am development program, resulted in an engine with 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. 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).

First
Year		 Last
Year		 Engine
Code		 Features Compression
ratio		 Power
Rating
1966 1969 L36 4-barrel 10.25:1 390 hp (291 kW)
1966 1966 L72 4-barrel + solid-lifters 11.00:1 425 hp (317 kW) [1]
1967 1969 L68 3x2-barrel 11.00:1 400 hp (298 kW)
1967 1969 L71 3x2-barrel + solid-lifters 11.00:1 435 hp (324 kW)
1967 1969 L89 L71 + aluminum heads 11.00:1 435 hp (324 kW)
1967 1969 L88 L72 + aluminum heads 12.50:1[2] 430 hp (321 kW)[3]
1969 1969 ZL1 All aluminum engine with open chamber heads 12.25:1 430 hp (321 kW)[4]
1970 1977(?) ZLX L88-ZL1 hybrid 12.25:1 430(?) hp (321 kW)[5]

Notes:

  1. ^ Chevrolet actually advertised this engine as 450 hp (336 kW) for a short period of time. There is speculation if this engine actually put out 450 hp, or if this was a marketing mistake 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 at 5200 rpm. Actual red line was 6400 rpm however, resulting in over 500 hp. With free-flowing headers and operation in the 7000 RPM range, it was generally accepted that the engine was capable of 550 hp.
  4. ^ Actual HP is not known for ZL1, but is accepted to have exceeded that of the L88
  5. ^ ZLX sold as a complete engine by selected dealers, or as a short block assembly, to which the purchaser would add the ZL1 heads, intake manifold and water pump. The factory recommended redline for this model was 7600 RPM, but 8000+ RPM was routine in competition. Like the L88 and ZL1, the actual HP was never quote by Chevrolet.

[edit] 454

The big-block was expanded again for 1970 to 454 in³ (7.4 L) with a 4.251 in (108 mm) bore and 4 in (102 mm) stroke. The 1970 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 is generally accepted that the LS6 was substantially underrated (a common practice at the time to avoid undue attention from insurance companies) and actually produced well over 500 horsepower as delivered from the factory. This notion was supported by the fact that an LS6 powered 1970 Corvette, in full street trim (including tires), was capable of accelerating from a standstill to 60 miles per hour (96 kilometers per hour) in less than four seconds, and covering a standing quarter-mile in little more than 12 seconds. Top speed was well over 160 miles per hour (256 kilometers per hour).

A 465 hp (347 kW) and 490 ft·lbf (664 N·m) version of the 454, dubbed LS7, was also produced, but was only available as a stand-alone or dealer-installed engine. Actually capable of some 600 horsepower when optimally tuned, the LS7 was probably the most powerful production automobile engine ever manufactured in the USA.

Power began falling off after 1970, with the 1971 LS5 producing 365 hp (272 kW) and 465 ft·lbf (630 N·m), and the LS6 option coming in at 425 hp (317 kW) and 475 ft·lbf (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 ft·lbf (529 N·m). The 1973 LS4 produced 275 hp (205 kW) and 390 ft·lbf (529 N·m), with 5 hp (4 kW) and 10 ft·lbf (14 N·m) gone the following year. 1974 was the last year of the 454 in the Corvette.

GM continued to use the 7.4 L 454 in their truck line, introducing a new Vortec 7400 version in 1996.

[edit] Commercial Applications

Mark IV engines saw extensive application in Chevrolet and GMC medium duty trucks, as well as in Blue Bird Corporation All American and TC/2000 transit buses (the latter up until 1995, using a purpose-built, carbureted 427). In addition to the 427, a 366 cubic inch (6.0 liter) version was produced for the commercial market. Both the 366 and 427 commercial versions were built with a raised deck cylinder block to accommodate an extra oil control ring on the pistons.

Mark IV engines also found themselves widely used in power boats, a natural application for these robust power plants. Many of these engines were ordinary Chevrolet production models that were fitted with the necessary accessories and drive system to adapt them to marine propulsion. Mercury Marine, in particular, was a major user of the Mark IV in marine drives, and relabeled the engines with their corporate logo.

[edit] 8100

A substantially-modified version of the 454 is sold today as the Vortec 8100.

[edit] References

  • Peter C Sessler (1999). Ultimate American V8 Engine Data Book. MotorBooks/MBI Publishing Company. ISBN 0-7603-0489-0.

[edit] See also

From the 1950s through the 1970s, each GM division had its own V8 engine family. Many were shared among other divisions, but each design is most-closely associated with its own division:

GM later standardized on the later generations of the Chevrolet design:

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