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Link titleThe 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.

Mark I Series
The first ever production big-block V8 Chevrolet engine was at first called the "W" series (later renamed the Mark I), 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 cuin, available from 1958 to 1961 in cars and through 1964 in trucks; 409 cuin, available from 1961 to 1965; and 427 cuin, available only in 1963.

As was the norm at the time, the "W" engine was of cast iron construction. The block had 4.84 in 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 lb, depending on intake manifold and carburetion, and was a physically massive engine compared to its small block predecessor.

348
The first iteration of the "W" engine was the 1958 "Turbo-Thrust" 348 CID originally intended for use in Chevrolet trucks, but also introduced in the larger, heavier 1958 passenger car line. Bore was 4.125 in and stroke was 3.25 in, 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. A special "Tri-Power" triple-two-barrel version, called the "Super Turbo-Thrust" produced 280 hp. A "Special Turbo-Thrust" upped the output to 305 hp with a single large four-barrel. Mechanical lifters and the three two-barrel carburetors brought the "Special Super Turbo-Thrust" up to 315 hp. For 1959 and 1960, high-output versions of the top two engines were produced with 320 hp and 335 hp respectively. In 1961, power was again increased to 340 hp for the single four-barrel model, and 350 hp when equipped with three two-barrels.

409
A 409 CID 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 by 3.50 in. 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, with a single-four-barrel Carter AFB carburetor. The same engine was upped to 380 hp 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 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 Mark IV big-block engine. In addition, a 340 hp 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)
A special 427 Cubic Inch 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 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 and 435 lbft. 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.

Mark II Series
The Mark II Series big-block Chevrolet engine was called the "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. It had canted valves in the head which had never been seen before. It also moved the combustion chamber out of the block and into the head, which produced a better volumetric efficiency at higher RPM. This produced better 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. The Mark II's displacement was 427 cubic inches.

Mark III Series
This engine series was never made for production use.

Mark IV Series
Development of the Mark IV 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.

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 lb. 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 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 crankshsft). 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. 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 was used only in Chevrolet Medium duty trucks and in school buses. This engine was made from the 1960's until the mid 1990's. The 366 used 3 compression rings on the pistons as it was designed from the very beginning as a truck engine. The 366 is a tall deck motor

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 by 96 mm), and produced 425 hp and 415 lbft. 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. Despite the fact that it was 6 CID larger, Chevy 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:


 * 1965: 375 hp/425 hp
 * 1966: 325 hp/350 hp/360 hp/375 hp
 * 1967: 325 hp/350 hp/375 hp
 * 1968: 325 hp/350 hp/375 hp
 * 1969: 265 hp(2bbl)/325 hp/350 hp/375 hp
 * 1970: 330 hp/350 hp/375 hp
 * 1971: 300 hp
 * 1972: 240 hp

Used in:


 * 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

427
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 in, 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.

Chevrolet produced the Big Block 427 until the mid 1990's. The only 427 available from 1972 to 1995 was a truck version that was used in GM medium duty trucks such as the Chevrolet Kodiak and GMC Top Kick until 1995. Throttle body electronic fuel injection was used on the 427 from 1988 to 1995.

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 hp version of the 427&mdash; (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 hp L71 version available in 1967 to 1969 Corvettes, and in the Italian Iso Grifo. This engine was identical to the 425 hp L72 427 (first introduced in 1966) but was fitted with three two barrel carburetors (known as "Tri-Power") 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 mi/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 While this option produced no power advantage, it did reduce engine (and hence, vehicle) weight by roughly 75 lb. 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 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, used an unshrouded radiator and had poor low speed idle qualities - all of which made the two engines largely unsuitable for street use. [102 octane RON (Sunoco 260) represented the highest octane gasoline sold at common retail stations.]

As 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 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. Chevrolet gave all 427 engines except the ZL1 a torque rating of 460 lbft.


 * 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)

454
The big-block was expanded again for 1970 to 454 cubic inches (7.4 L) with a 4.251 in bore and 4 in stroke. The 1970 Chevy Corvette LS5 version of this engine produced 390 hp and 500 lbft, and the LS6 engine was rated at 450 hp. It has been suggested that the LS6 was substantially underrated and actually produced well over 500 hp 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 mi/h "1970 ASA LS6 454 Records", which suggests something on the order of 370 "as installed" (SAE Net) HP for a 3900 lb car and driver combination.

A 465 hp and 490 lbft 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 few Chevy dealers as performance parts. The LS7 was later offered as a crate engine from GM and advertised at 500 hp.

Power began falling off after 1970, with the 1971 LS5 producing 365 hp and 465 lbft, and the LS6 option coming in at 425 hp and 475 lbft. Only the LS5 remained in 1972, when SAE net power ratings and the move towards emission compliance resulted in to 270 hp and 390 lbft. The 1973 LS4 produced 275 hp and 390 lbft, with 5 hp and 10 lbft 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. The 454 EFI version was rated from 230 hp to 255 hp and from 385 lb.ft to 405 lb.ft of torque. 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

502
The 502 CID 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 to 502 hp, and torque of 470 lbft to 567 lbft in "Base" and "Deluxe" packages. The "Ram Jet 502" (502 hp / 565 lbft) 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.

572
Chevrolet began offering a 572 CID "crate motor" in 2003 which produced 720 hp and 685 lbft of torque, and more recently a 620 hp / 650 lbft version capable of running on 93 octane street gasoline.

Gen VII Series
The Vortec 8100 7th generation (known as gen VII) Chevrolet big block, has the same bore as a 454 (4.25 inches), but has a stroke of 4.37 in. It is similar to the smaller GM LS engine family in that it has coil-on-plug ignition and a 1-8-7-2-6-5-4-3 firing order. It was used in 3/4 ton and larger light trucks, and medium duty commercial vehicles. Produced in the years of 2001–2009.

The aftermarket
The large variety of aftermarket components manufactured for the big block family makes it possible to build a complete big block engine that contains no Chevrolet components. Blocks made of both iron and aluminum alloys are available in stock configurations and also with increased deck height to allow longer stroke or more favorable rod length ratios, providing the ability to make 632 CID engines, and larger.

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, four bolt main bearing cap cylinder to accommodate an extra oil control ring on the pistons. Unfortunately, the raised deck design complicated the use of the block in racing applications, as standard intake manifolds required spacers for proper fit. Distributors with adjustable collars that allowed adjustments to the length of the distributor shaft also had to be used with 366 and 427 truck blocks.

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.