Chevrolet manufactured two significant big-block engines in the second half of the twentieth century. It’s important to acknowledge and briefly examine them because the first-design big-block became a strategic player in the epic power struggle that erupted among domestic automakers in the early 1960s. It set a compelling performance precedent for the second-generation Markseries big-block engines. I refer of course to the Mark I Chevrolet “W” engine, a celebrated engine in its own right. This unique design, introduced in 1958, provided a smooth-idling high-torque engine for GM trucks and the larger, heavier, and more glamorous cars that the public demanded. Big cars implied elevated status. Everyone wanted one, but the early small-block still displaced only 283 ci and could not provide enough torque to move these bigger cars efficiently. Enter the first Turbo Thrust 348 W engine, which also significantly boosted the performance of Chevrolet and GMC trucks.
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W-series Mark I (Gen I) engines are the original Chevrolet big-blocks, built to power passenger cars and trucks across the Chevrolet lineup. They featured an overhead design with offset valves and the unique scalloped valve covers that prompted the “W” moniker. They were produced from 1958 through 1965 in three different displacements. The original 348-ci (5.7L) engine was offered from 1958 through 1961 in cars and through 1964 in trucks. In 1961 the engine gained 61 ci, becoming the fabled 409 (6.7L) celebrated in song by the Beach Boys. (Who doesn’t remember “She’s real fine, my 409?” Every teenage driver in America coveted the 409.) The 409 was offered from 1961 through 1965 and was briefly supplemented by the one-off 427-ci RPO Z11 race engine available only in 1963. The original Chevrolet engineers have long lamented some of the design compromises inherent to the W engines and they labored to bring them up to speed. In some cases, inefficient combustion chambers, valve sizes, and cooling problems on some 348 versions limited performance. Despite numerous problems, these engines ultimately fulfilled their performance potential by moving to the nation’s drag strips and selected deserted roads during their brief, but surprisingly influential, tenure.
These first-generation big-blocks were built on 4.84-inch bore centers with two-bolt main bearing caps and interchangeable cylinder heads. Performance 409- and 427-ci versions incorporated larger ports and valves than the standard 348 and 409 base engines used in cars and trucks. All engines in this series incorporated a main oil gallery just above the oil pan rail on the driver’s side of the engine block (the same as on early Mark IV series V-8s). All W-series engines, including the fabled 427-ci Z11 package, have two-bolt main caps. One quick way to differentiate between 348s and 409s is by dipstick location; it’s on the driver’s side on all 348s and on the passenger’s side on 409s and the Z11 race engine.
W-series cylinder heads exhibit several distinct characteristics including offset valves (not inline) and unique if not downright odd wedge-shaped combustion chambers that incorporate part of the upper cylinder wall. The block deck surfaces are not perpendicular to the cylinder bores. This results in a uniquely beveled piston crown with a pronounced quench area intended to promote good mixture turbulence with a spark plug positioned to provide a fast burn. The resulting high brake mean effective pressure (BMEP) for that period at low engine speeds delivered a broad torque curve that provided exceptional performance in larger and heavier cars and trucks. Mark IV and later production engines have no commonality with W engines except that original Mark IV blocks (or later Bowtie blocks) with one-piece rear seals accept W-series crankshafts if spacer bearings are used to accommodate the difference in main bearing size.
Zora Arkus-Duntov (legendary Corvette designer and father of the GM performance culture) christened them Mark I engines to differentiate them from later-design big-blocks because he was still working on W-engine drag racing development while the all-new Mark II Mystery Motors and subsequent Mark IVs were in the design stage. The first-design Mystery Motor (there were actually three versions) incorporated the 409-ci W-engine bore and stroke and the 427-ci Z11’s 6.135-inch rod length, all wrapped up in a brand-new cylinder block designed to accept the new canted-valve heads. If you know your history, it’s easier to follow Mark IV and later engine progression.
From a performance standpoint nearly all W engines were rated at more than 300 hp. Among the 348 offerings were four Tri-Power versions delivering 280, 315, 335 hp, and the best of the bunch with 350. Many 409 engines were offered, ranging from a 360-hp single 4-barrel unit to a 425-hp dual 4-barrel powerhouse.
The special 427-ci RPO Z11 race version (1963 only) was rated at 430 hp with a longer 3.65-inch stroke, 13.5:1 compression ratio (CR), and dual Carter AFB carbs similar to the 425-hp versions. Records suggest that this engine actually delivered more than 500 hp and was installed in approximately 50 factory-built Z11 race cars. Twenty partial engines were also produced for replacement purposes and they are nearly impossible to find today.
These Gen I or W-series engines provided a formidable performance stepping stone from the small-block V-8 to the Mark IV big-block engine. Today, the same bore spacing and beefy architecture prevails with basic dimensions that allow big-blocks to be built with stroke lengths ranging all the way to 4.75 inches and in some cases even longer. Performance big-blocks and their spectacular racing history reinforce the performance legacy of the original W engines, whose accomplishments on the drag strips and banked ovals in the early 1960s established an impressive Chevrolet stronghold on motorsports activity in the United States.
Gen II, the Mark Series
The Mark II second-generation bigblock began life in the summer of 1962 under the direction of Chevrolet engineer Dick Keinath. It has often been called an upgrade or a revision of the W engine, but that is incorrect. The Mark II was a “clean sheet” racing engine design that only incorporated a few remotely related design cues from earlier W-series engines. Among them the same 4.84-inch bore center dimension, the main oil gallery location adjacent to the driver-side oil pan rail, race-style Moraine M400 aluminum bearings from the 409, and the basic 409 crankshaft. Initially it was an allnew 409-ci engine designated the Mark II to clearly differentiate it from earlier W-series engines. The old saying that racing improves the breed definitely holds true for the big-block Chevy.
The Mark II (RPO Z33) V-8 was designed for racing on high-banked NASCAR tracks where top speed is paramount, but designers knew from the very beginning that this engine would ultimately power the next generation of Chevrolet trucks and passenger cars, so parallel development was carried out from day one. It is interesting that Mark II development engineer Billy Howell says that he has never heard of the RPO Z33 designation and is not confident about where it came from. It may be legit or it may be part of the unverified nostalgic lore that surrounds these remarkable engines.
This engine was destined to set the stock car world on its ear with its debut at the 1963 Daytona 500. A Ford ultimately won the race that year, but the mind-blowing speeds recorded by Junior Johnson, Johnny Rutherford, Smokey Yunick, Ray Fox, and Bubber Farr stunned the competition. Junior Johnson qualified on the pole thanks to blistering speed and served notice to the competition that Chevrolet was in the house with a “Mystery Motor” designed to tear them a new one.
The big secret of the mysterious engine was its cylinder head design. It had unique offset canted valves that opened away from the cylinder walls to improve cylinder filling by unshrouding the valves. It was called the “porcupine” because the valvestems appeared to stick out in all directions much like the quills on a porcupine. The “chamber-in-block” design of the W engine favored low- and mid-range torque production, but lost efficiency at higher engine speeds, particularly at racing RPM.
A more conventional bathtub chamber with unique compound valve angles provided superior high-speed breathing and efficiency to support the racing effort. They effortlessly served the desired low-speed performance with higher CRs and revised inlet and exhaust tuning. By incorporating Chevrolet’s trademark stud-mounted rockers the canted valves were easily activated by unequal-length pushrods that remained stable at racing speeds. Spark plug location was revised with an angle plug design entering the cylinder tangentially. This further improved high-speed combustion efficiency and eliminated the need for the W-style valve covers to accommodate spark plug placement on earlier engines.
According to Smokey Yunick, at least 50 of the original Mark II engines were built, this statement seems entirely plausible given in-house testing requirements and additional outside development performed by racers including Smokey and Junior Johnson. Howell concurs with Smokey’s assessment; nevertheless, few can be found today.
In 1963, Chevrolet initiated a Mark II design study as part of the secondgeneration passenger car and truck Mark engine development. This study briefly surfaced as a Mark III big-block design using wider bore centers to accommodate larger cylinder bores and larger valve sizes along with more favorable intake runner positioning and port entry angles. In the end this project never materialized because tooling costs for the new block and accompanying hardware were deemed excessive. If the design had flourished, subsequent big-blocks may well have been even more powerful. As it was, the basic Mark II architecture was refined for road use and launched into production in 1965 as the Mark IV 396-ci engine; the top power rating was 425 hp.
Except for displacement the Mark IV remained relatively unchanged for the next 25 years. It established itself as the most respected large-displacement performance engine for racers, rodders, and towing applications. Ironically, decades later, private big-block race engine developers, such as Sonny’s Racing Engines, adopted wider bore spacing and complementary heads for their Pro Mod race engines and realized the significant power gains some Chevrolet engineers had envisioned back in 1963.
The new Mark IV big-blocks had some component-similarity with previous W-series engines. Among the shared features were an appropriate mix of cast and forged pistons per specific horsepower requirement and the surprisingly useful crankshaft compatibility. All Mark IV bigblocks have 2.75-inch main journals with production stroke lengths ranging from 3.76 to 4.25 inches. Shorter-stroke Mark IV engines can be built (or destroked) using earlier 348 or 409 forged crankshafts with appropriate spacer bearings. This little-known direct swap was first adopted in the early days of 500-ci Pro Stock racing as racers explored bigbore short-stroke combinations. No longer used for that application, this swap is still employed in selected drag racing classes. It is particularly popular at Bonneville, where superior-breathing Mark IV big-blocks are sometimes destroked with forged W-engine cranks to build high-RPM small-displacement big-blocks that breathe like crazy to meet particular class displacement limits.
Designer Dick Keinath sets the record straight by confirming that only the crankshaft in the Mystery Motor interchanges with the W engines or Mark IV big-blocks. Although the engine is visually almost identical to the Mark IV series it spawned, Keinath relates that port locations and alignment are different, bolt hole locations are not the same, and some cooling passages are not the same. During its concurrent development, the Mark IV engine underwent numerous revisions to accommodate manufacturing and production requirements.
Basic Engine Architecture
The Chevrolet Mark-series big-block is a traditional V-8 with unique design features. It is not based on the earlier 348/409 W-series engines, but it does incorporate some minor design cues from both. As such, it is possible to fit earlier W-series crankshafts into Mark IV blocks to achieve small-displacement “destroked” engines for favorable class placement in some racing series. Mark-series V-8 architecture incorporates two banks of four cylinders set at an opposing angle of 90 degrees. The bore spacing between cylinders measures 4.84 inches on centers, and the deck surfaces remain a conventional 90 degrees perpendicular to the centerline of the cylinder bores. The crank centerline is set at the bottom of the block almost even with the oil pan rails as it is on the small-block and previous W-series engines.
The standard engine’s deck height measures 9.80 inches from the crank centerline to each deck surface. Tall-deck truck versions measure 10.2 inches to accommodate taller pistons with one additional compression ring added to promote stability and enhance cylinder sealing. The canted-valve cylinder heads are the main feature of these engines and the reason they breathe so well in performance applications. The offset canted-valve placement requires separate pushrod lengths for the intake and exhaust valves. All engines use 6.135-inch connecting rods that yield a range of rod-to-stroke ratios from 1.53 to 1.63 depending on deck height, stroke length, and pin height. All Mark IV and later big-blocks have 2.75-inch main journals and 2.2-inch rod journals. General engine construction is robust and these engines typically have no problem revving to high RPM with appropriate valve gear. The cranks are tough too; the mains are beefy and the cylinder heads promote stump-pulling torque and serious power when properly matched to the engine application.
Understanding RPO Codes
Big-block Chevys are built in many different sizes and configurations, all designated by Regular Production Option (RPO) codes. Each one defines a specific build applied to any particular vehicle or engine series. In some cases the RPO code refers to a vehicle/engine combination such as the 1965 Z16 Chevelle. Z16 was the code for Chevelles equipped with the 375-hp 396-ci V-8 engine and specified accompanying components such as a 4-speed transmission. As engines go, most RPO codes refer to that particular engine without necessarily specifying its vehicle usage. RPO codes were created for easy in-house referral to various packages, but enthusiasts have adopted and elevated many of them to legendary status well beyond their humble intent; the L88 Corvette package for example.
Broad availability of present-day factory and aftermarket big-block parts has rendered RPO codes all but irrelevant for big-block power users. The exception, of course, is for restoration enthusiasts seeking to recombine factory-built packages that may have been scattered to the wind back when the value of factory performance parts was largely unappreciated. For the most part superior performance is easily obtainable from more current hardware, but RPO packages remain an essential component of any serious restoration effort. This explains the rarity of many early parts and the inevitable escalation of their value.
Listed below are performance-related RPO engine codes. They are primarily for reference and to help identify characteristics of various big-block engine combinations you may be fortunate enough to stumble across while trolling for engines and parts.
The following RPO codes are relevant to most popular big-blocks, but they do not address all the big-blocks offered over the years. For example, in 1973, Monte Carlos, Chevelles, full-size passenger cars, and light-duty trucks could be ordered with a 215-hp 454 V-8. The last big-block Corvette was sold in 1974 and the last big-block Chevelles, Monte Carlos, and full-size cars set sail in 1975. From 1976 on, standard 454 shortdeck big-blocks were reserved for lightduty trucks only. The primary Mark IV engine from 1973 to 1987 was the RPO L-19 454 truck engine with 8.25:1 CR, 215-hp 454, with either two- or four-bolt mains, steel or cast crank, cast pistons, 3/8-inch-diameter rod bolts, openchamber oval-port heads, 5/16-inch pushrods, hydraulic cam, and a Q-Jet carb atop a cast-iron low-rise intake manifold. Lots of them are out there.
From 1988 to 1990 the Mark IV lost the carburetor and gained throttle-body injection (TBI). It provided 230 hp at 3,600 rpm and 385 ft-lbs of torque at 1,600 rpm. The Gen V (RPO L-29) version debuted in 1991 and was also fitted with TBI. The Gen VI Vortec 7400 454 surfaced in 1996 with sequential fuel injection and more powerful roller cam profiles. The 1996 and later Gen VI Vortec series (RPO L18) 454 big-blocks delivered 290 hp at 4,200 rpm and 410 ft-lbs of torque at 3,200 rpm. They all have 9:1 CR, four-bolt mains, sequential port fuel injection with a mass airflow meter, two-piece aluminum intake with tunedlength runners, round-port Gen VI cylinder heads with the refined 100-cc Vortec combustion chambers, and a more aggressive hydraulic roller cam. They retain all the desirable features of earlier Mark IV engines and they have been around long enough that there is no shortage of good cores.
396-ci V-8 RPO Codes
Seven versions of the new 396-ci Mark IV big-block engine were produced between 1965 and 1969. The 396 has a bore and stroke of 4.094 x 3.76 inches and was produced with both two- and four-bolt main caps right from the beginning. There are five basic RPO codes assigned to 396 engines.
1966–1969, 396 ci, 350/360 hp at 5,200 rpm, two-bolt mains (four-bolt, 1966), forged-steel crank, cast pistons, closed-chamber oval-port heads, 10.25:1 CR, high-lift hydraulic cam, Holley 4V (1966–1968), Q-Jet (1968–1969), cast-iron high-rise intake manifold. Used in full-size cars, Camaros, and Novas through 1972.
1965–1967, 396 ci, 325 hp at 4,800 rpm, 10.25:1 CR, two-bolt mains, forgedsteel crank through 1967, cast pistons, closed-chamber oval-port heads, Holley 4V carburetor (PN 3874898), and castiron intake manifold or Rochester (PN 7026201) Q-Jet carburetor with cast-iron intake. Used in Camaros and Chevelles from 1966 through 1970.
1965, 396 ci, 375 hp at 5,600 rpm, RPO Z16 Chevelle package, same as L78 but with high-lift hydraulic cam, highrise aluminum intake manifold, and 780- cfm Holley 4V carburetor (PN 3893229).
1969, 396 ci, 265 hp, two-bolt mains, steel crank, 3/8-inch rod bolts, cast pistons, closed-chamber oval-port heads, 9:1 CR, 2V carb, cast-iron intake manifold. Used in full-size passenger cars and station wagons.
1965–1969, 396 ci, 375 hp at 5,600 rpm in mid-size cars, 425 hp at 6400 rpm in Corvettes, 11:1 CR, four-bolt mains, forged-steel tuftrided crank, forged pistons, closed-chamber rectangular-port heads, solid lifter cam (same specs as L-72 427 except in 1965 RPO Z16 Chevelle), high-rise aluminum intake, 800-cfm Holley 4V carburetor.
1965, 396-ci, 425-hp Corvette and passenger car, exact same as 375-hp 396 L78 with solid cam.
1968–1969, 396 ci, 375 hp, same as L78, but with optional closed-chamber square-port aluminum heads, high-lift solid cam for use in Camaros and Novas.
1969, 396 ci, 265 hp at 4,800 rpm, 9:1 CR, nodular iron crank, cast pistons, closed-chamber oval-port heads, hydraulic cam, cast-iron intake manifold, and 2-barrel carburetor for use in Chevelles and full-size cars.
402-ci V-8 RPO Codes
All 402-ci big-blocks were virtually identical to their 396 counterparts except the bore diameter was increased to 4.125 inches. 350-hp L-34 versions had twobolt mains; the 375-hp L-78 versions were equipped with four-bolt mains. These engines were equipped the same as their 396-ci counterparts.
1970, 402 ci, 330 hp, 10:25:1 CR, nodular iron crank, cast pistons, closedchamber oval-port heads, hydraulic cam, cast-iron intake manifold, and Q-Jet carburetor for use in Chevelles and full-size cars. 1971, 402 ci, 300 hp, 8.5:1 CR, exact same as above, but with open-chamber oval-port heads.
1972, 402 ci, same as above except 210 net hp with single exhaust or 240 net hp with dual exhaust.
1970, 402 ci, 350 hp at 5,200 rpm, 10.25:1 CR, 4.125-inch bore, same stroke as 396 ci, two-bolt mains, some four-bolt mains, steel crank, 3/8-inch rod bolts, cast pistons, closed-chamber oval-port heads, high-lift hydraulic cam, Q-Jet carburetor.
1970, 402 ci, 375 hp at 5,600 rpm, exact same as 375-hp 396 except larger 4.125-inch bore.
427-ci V-8 RPO Codes
Eight primary RPO codes were assigned to 427-ci big-blocks with additional versions based on tall-deck truck applications.
1966–1969, 427 ci, 385 hp in fullsize cars, 390 hp in Corvettes, 10.25:1 CR, same basic content as L34 396 except larger 4.25-inch bore, two-bolt mains, cast pistons, cast crank, closed-chamber oval-port heads, high-lift hydraulic cam, Q-Jet carburetor, cast-iron intake manifold, aluminum low-rise intake manifold, Q-Jet carburetor on 1968–1969 Corvettes.
1967–1969, 427 ci, 400-hp Corvette engine, 10.25:1 CR, same as L-36 except oval-port aluminum intake manifold, three 2V carburetors.
1967–1969, 427 ci, 435 hp at 5,800 rpm, 11:1 CR Corvette engine only, same as L72 except four-bolt mains, steel tuftrided crank, forged pistons, closed-chamber square-port heads, solid cam, square-port aluminum intake manifold, three 2V carburetors.
1966–1968, 427 ci, 425 hp at 5,600 rpm, 450 hp in some Corvettes, 11:1 CR, four-bolt mains, steel tuftrided crank, forged pistons, closed-chamber square-port heads, solid cam, aluminum high-rise intake manifold, Holley 800-cfm carburetor.
1967–1969, 427 ci, 430 hp, 12.5:1 CR, four-bolt mains, steel tuftrided crank, 7/16-inch-diameter “dot” rods, forged full-floating pistons, 1/16-inch rings, solid cam, closed-chamber square-port aluminum heads (1967–1968), open-chamber square-port aluminum heads (1969), 7/16-inch-diameter pushrods, Holley 850-cfm carburetor on aluminum highrise intake manifold with cut-down center divider. Generally known to have made more than 550 hp at 6,400 rpm as related in Hot Rod magazine and other performance publications of the period.
1968, 427 ci, 425-hp Corvette engine only, exact same as L-71 but with optional closed-chamber square-port aluminum heads.
1969, 427 ci, 335 hp, 10.25:1 CR, two-bolt mains, nodular iron crank, closed-chamber oval-port heads, hydraulic cam, high-rise cast-iron intake manifold, Q-Jet carburetor. Offered in mid-size cars only.
1969, 427 ci, 430 hp, 12.5:1 CR, aluminum block with four-bolt mains, steel tuftrided crank, 7/16-inch-diameter “dot” rods, forged full-floating pistons, 1/16-inch rings, solid cam, closed-chamber square-port aluminum heads (1967–1968), open-chamber square-port aluminum heads (1969), 7/16-inch-diameter pushrods, aluminum high-rise intake manifold with cut-down center divider, Holley 830-cfm carburetor.
Same content as L88, 2 installed in Corvettes, 69 installed in Camaros, and unknown number sold over the counter.
454-ci V-8 RPO Codes
1970; 454 ci; 345 hp at 4,600 rpm, 275 net hp at 4,400 rpm in 1973 Corvettes, 270 net hp in 1974 Corvettes, and 245 net hp at 4,000 rpm in full-size cars; 10.25:1 CR; two-bolt mains; steel crank; cast pistons; hydraulic cam; closedchamber oval-port heads; cast-iron intake manifold; Q-Jet carburetor. 1973–1974; 454 ci; 9:1 CR; 215, 235, 245, 270 hp; cast pistons; hydraulic cam; open-chamber oval-port heads; cast-iron intake manifold; Q-Jet carburetor.
1970; 454 ci; 390 hp in 1970 Corvettes, 360 hp in Monte Carlos and Chevelles; 10.25:1 CR; two- or four-bolt mains; steel crank; cast pistons; hydraulic cam; closed-chamber oval-port heads; low-rise cast-iron intake manifold, Q-Jet carburetor.
1971, 454 ci, 365 gross hp, 285 net hp, 8.5:1 CR, two- or four-bolt mains, steel crank, cast pistons, hydraulic cam, open-chamber oval-port heads, lowrise cast-iron intake manifold, Q-Jet carburetor. 1972, 454 ci, 240 hp with single exhaust, 270 hp with dual exhaust, 8.5:1 CR, two- or four-bolt mains, steel crank, cast pistons, hydraulic cam, open-chamber oval-port heads, low-rise cast-iron intake manifold, Q-Jet carburetor.
1970; 454 ci; 450-hp Chevelle engine, 460 hp in Corvette; 11:1 CR; four-bolt mains; steel tuftrided crank; 7/16-inch bolt diameter “dot” rods; forged pressed pin pistons; closed-chamber square-port heads; solid cam; high-rise aluminum intake manifold; Holley 800-cfm carburetor. 1971, 454 ci, 425-hp Corvette engine, 9:1 CR, four-bolt mains, steel tuftrided crank, 7/16-inch bolt diameter “dot” rods, forged pressed pin pistons, open-chamber square-port aluminum heads, solid cam on high-rise aluminum intake manifold, Holley 800-cfm carburetor. Monte Carlo and Chevelle were to get same engine except with cast-iron open-chamber square-port heads.
1970, 454 ci, 465 hp, 12.5:1 CR, four-bolt mains, forged steel tuftrided crank, 7/16-inch bolt diameter “dot” rods, forged full floating pin pistons, open-chamber square-port aluminum heads, high-lift solid cam, 1/16-inch rings, 3/8-inch pushrods, high-rise aluminum intake manifold with cut-down plenum divider, 830-cfm carburetor. Originally intended for 1970 Corvette, but it was never installed in a production car. It was made available as a crate engine assembly or it could be built with available over-the-counter parts.
1986–1989, 454 ci, 240 net hp, lowdeck truck engine only, two- or four-bolt mains, small oval-port (peanut) cast-iron heads, cast-iron crank, hydraulic cam, castiron intake manifold, Q-Jet carburetor.
1987–1989, 454 ci, 230 net hp, lowdeck truck engine only, first computercontrolled 2-barrel TBI, two- or four-bolt mains, replaced RPO LE8, peanut-port cast-iron heads, hydraulic cam, cast crank and pistons. This was the final production Mark IV engine.
L19, 7.4L Gen V
1991–1995; 454 ci; 230 net hp; trucks only; two- or four-bolt mains; same as previous L19 except Gen V block and crank with one-piece rear main seal, peanut-port heads, TBI, hydraulic cam.
L19/L29, 7.4L Gen VI (Vortec 7400)
1996–2000, 454 ci, 290 net hp, trucks only, four-bolt mains, MPFI multiport fuel injection, hydraulic roller cam, peanut-port cast-iron heads, cast crank and pistons.
1998–2001, 454 ci, 265/270 hp at 3,200 rpm, commercial trucks only, commonly called the 7400 MD, four-bolt mains, forged crank and pistons, new PCM control module for use with Allison 4-speed automatic or 4-speed manual, MPFI, hydraulic roller cam, peanut-port cast-iron heads for medium-duty trucks. Workhorse Custom Chassis, Kodiak/ Topkick series.
L18 8.1L Gen VII
2001–2006, 496 ci, 225/340 net hp, trucks only, four-bolt mains, symmetrical port heads with all-new 18-bolt pattern, tall-deck block, distributorless coil-nearplug ignition, redesigned MPFI, hydraulic roller cam, same 4.25-inch bore with longer 4.37-inch stroke and revised fi ring order of 1-8-7-2-6-5-4-3.
Tall-deck 366- and 427-ci big-blocks were manufactured from 1966 through 1995 for use in medium- and heavyduty trucks, school buses, and some partial chassis sold to manufacturers of motorhomes. They’re tough, reliable, and they make a great starting point for a race engine. From 1991 to 1995 Chevrolet switched to the Gen V block confi guration. If you acquire one of these blocks for performance use bear in mind that it does not have a mechanical fuel pump boss.
Tall-deck blocks are .40 inch taller (10.2 inches) than standard short-deck (9.8 inches) big-blocks to accommodate heavy-duty truck pistons with thicker piston crowns and a ring package consisting of three compression rings and one oil ring. Mark IV versions accept all Mark IV cylinder heads and they require matching tall-deck intake manifolds. Gen V versions accept Mark IV heads if the proper head gasket is used. This holds true for standard-deck aftermarket intake manifolds (with spacers), but most manufacturers now offer tall-deck versions of their best short-deck manifolds thus relieving the need for spacers. Note that because of the longer stroke, Chevrolet’s 572-ci crate engine is a tall-deck engine.
Taller decks move the heads farther apart resulting in tall-deck-only intake manifolds, but standard-deck manifolds can be used with the correct spacers. Spacer kits to use standard short-deck manifolds on tall-deck blocks are available from Weiand. The spacer plates are .375 inch thick and each spacer requires two intake gaskets. Oval-port spacers carry part number 8206 and the squareport spacer kit is part number 8204. Note that when using spacers on tall-deck blocks, an aftermarket adjustable-height distributor is required to ensure proper engagement with the cam gear.
When used for racing and highperformance applications tall-deck blocks lend themselves handily to stroker applications. They also provide the opportunity to jockey rod length, piston compression height, and ring position to suit your specifi c needs. Because they are intended for heavy-duty use, all tall-deck blocks have four-bolt mains, extra-thick cylinder walls, and provisions for oil coolers. If you plan a stroker application with one of these blocks make sure you check for adequate pan rail clearance, as these blocks are not relieved for strokers. Also note that raised cylinder heads alter header or exhaust manifold location in the engine compartment, possibly leading to fi tment issues.
Tall-deck combinations are plentiful. You can build a broad variety of stroker combinations wrapped in a heavyduty package that is both powerful and durable. If you’re starting from scratch consider a Bowtie tall-deck block that is already confi gured to accept stroker cranks without interference problems. Moreover, if you’re handy with a calculator you can brainstorm pin height, rod length, and stroke length to discover new and potentially benefi cial combinations. Remember, at the top of the stroke you have to factor in some reasonable combination of rod length, one-half of the stroke length, and a piston pin compression height that fi ts within the established deck height and accommodates the ring package you intend to use.
This varies according to application. For example, turbo applications typically move the ring package lower on the piston to combat excessive heat. This often moves the ring pack into the pin bore location and provisions must be made to ensure compatibility. Your piston manufacturer can help you with this if you’re not comfortable with it.
Big-Block Crate Engines
Chevrolet Performance big-block crate engines offer top-level over-thecounter performance for almost any bigblock application you can think of except perhaps max-effort class racing engines. Because the lineup also includes partial engine assemblies, racers and rodders are free to mix and match factory and aftermarket components to achieve any level of performance they desire. Plenty of used crate engine deals are available that can provide good service with a little refurbishing. Most crate engines already incorporate performance hardware including forged cranks and pistons, heavy-duty rods, roller cams, and high-performance aluminum heads. The selection and range of performance options has never been more favorable for those seeking to rebuild or upgrade a solid, reliable big-block.
The following crate engines are currently available (2013) and they comply with all known big-block compatibility issues.
ZZ427/480 hp (PN 19166393)
480 hp at 5,800 rpm, 490 ft-lbs at 3,800 rpm The 480-hp ZZ4 427 is Chevrolet’s iteration of the former L88 427. It is built with an iron four-bolt block (PN 19170538), forged steel crank, and high-flow aluminum cylinder heads. Gen V upgrades applied to this engine include a one-piece rear main seal and a milder hydraulic roller cam for smoother street operation. The cam measures 224/234-degrees duration at .050 inch with .527-inch intake lift and .544 inch on the exhaust. The crankshaft and rods are forged steel and the forgedaluminum pistons net 10:1 compression for premium-fuel compatibility. It uses the standard 4.25/3.75-inch bore and stroke with one-piece rear main seal. The oval-port high flow aluminum cylinder heads (PN 19211799) carry standard 2.19/1.88-inch intake and exhaust valves with premium valvesprings and 1.7-ratio rockers. The engine breathes through an aluminum 4-barrel intake capped with an 870-cfm Holley carburetor. It also comes equipped with an aluminum water pump, HEI (high energy ignition) distributor, SFI-approved crankshaft dampener, spark plug wires, and a 14-inch-diameter flexplate.
Anniversary Edition 427 (PN 19166392)
430 hp at 5,800 rpm, 444 ft-lbs at 3,800 rpm The limited-edition Anniversary Edition 427 is essentially the same as the ZZ427 except that it is built with a Gen VI aluminum block (PN 88958696). This lightweight version is personalized with serialized cast-aluminum valve covers. Whereas the ZZ427 is representative of a modern-day L88, the Anniversary Edition 427 pays homage to the legendary ZL1 aluminum big-block.
It features a forged-steel crank and rods with forged pistons. It uses the same hydraulic roller cam (PN 12366543) and oval-port aluminum heads (PN 19211799), 2.19/1.88-inch valves, and aluminum roller rockers (PN 12361323). Chevrolet describes it as mimicking the original ZL1 in spirit while incorporating pump-gas-friendly tweaks that still provide great power with improved driveability.
They’re building only 427 copies and each numbered engine comes with a special owner’s kit and certificate of authenticity, special 427 emblems, and more. Note that Chevrolet still sells a replacement Mark IV–style ZL1 aluminum cylinder block that accepts the traditional two-piece rear main seal (PN 12370850). It can be used to build an authentic ZL1 replica if you so choose.
454 HO (PN 12568774)
425 hp at 5,250 rpm, 500 ft-lbs at 3,250 rpm The 454 HO crate engine is based on a cast-iron Gen VI block (PN 19170538) outfitted with rectangular-port cylinder heads (PN 12562920) sporting 118-cc combustion chambers and 8.75:1 CR. It uses a hydraulic roller cam with 210/230 degrees of duration at .050-inch lift, and .510/.540-inch intake and exhaust lift operating 2.19/1.88-inch valves. With forged 8.25:1 compression pistons, it is fully pump-gas compatible and a forged steel crank and rods make it a durable player. It is furnished with a water pump, crankshaft dampener, 14-inch flexplate, and aluminum performance intake manifold. The complete engine is sold without carburetor, ignition, or starter, but it provides the foundation for 500 ft-lbs of tire-wrinkling torque that seriously motivates anything you install it in.
The low-key all-iron look makes this super sleeper the perfect choice for a traditional-style street rod or street machine. And you can dress it out any way you like to maintain the sleeper image or jazz it up with trick valve covers, coated headers, performance air cleaner, and custom plumbing to give it a serious street engine flavor.
ZZ454 Partial Engine Assembly (PN 12498778)
This partial engine assembly delivers the basic Gen VI performance short-block used for the 454 HO performance engine. It includes a four-bolt block, forged internals with dampener, and oil pan. Add your preferred heads and induction system and build a powerful big-block to your own personal specs. This setup provides a sound foundation for a mild supercharged effort or a normally aspirated application with head selection to increase compression. Starting with this assembly you can plan dozens of hot combinations and decide which one is best for your ride.
ZZ454/440 (PN 12498777)
440 hp at 5,250 rpm, 500 ft-lbs at 3,250 rpm This engine uses the same performance-bred short-block as the Gen VI 454 HO and it takes on a set of oval-port aluminum cylinder heads (PN 12363392) with 110-cc combustion chambers. The smaller chambers raise the CR to 9.6:1, adding 15 hp. This crate engine package includes a water pump, dampener, aluminum intake manifold, and a 14-inch flexplate. If you prefer aluminum heads and 500-plus ft-lbs of torque this is the one you want.
HT502 Truck Replacement Engine (PN 88890534)
377 hp at 4,500 rpm, 512 ft-lbs at 3,300 rpm Here’s a high-torque Gen VI–style 502-ci monster combining a siamesed 4.47-inch-bore block (PN 19170540) with a forged 4-inch crank and production-style oval “peanut” port iron heads sized to maximize low-end torque. It’s the ideal choice for repowering your pickup or tow truck, maybe even dress it up for a smooth cruisin’ low rider. Designed for heavy-duty use in pre- 1978 trucks, it features forged rods, forged 8.75:1 CR pistons, and a mild hydraulic roller cam with 204/209 degrees of intake and exhaust duration at .050-inch lift and .480/.483-inch valve lift. It is fully pump-gas compatible and it comes with heads and a balancer installed. A complete Gen VI–compatible ignition and induction system, starter, water pump, and other accessories are required to get this baby up and running.
ZZ502/502 Partial Engine, Short-Block (PN 12568782)
This Gen VI–based short-block incorporates all the best components of the HT502 Truck Replacement Engine, but leaves room for fitting your choice of induction systems. Instead of the standard peanut-port heads you can install the performance heads of your choice and the accompanying induction and ignition system to boost power with confidence that the lower end will hold up well.
502 HO (PN 12568778)
450 hp at 5,250 rpm, 550 ft-lbs at 3,500 rpm The high-output 502 uses the Gen VI block with a 4.47-inch bore (PN 19170540) and rectangular-port cast-iron cylinder heads with 118-cc chambers (PN 12562920). It utilizes a hydraulic roller cam with 210/230 degrees of duration at .050-inch lift and .510/.540-inch intake and exhaust lift operating 2.19/1.88-inch valves. It features an all-forged rotating assembly with 8.75:1 compression. This engine is sold without a carburetor, distributor, or starter, but it does include the crank dampener.
If an aftermarket distributor is not used, Chevrolet Performance recommends its PN 93440806 distributor with a “melonized,” or hardened (see Chapter 8), steel gear that is fully compatible with hardened roller cam gears.
ZZ502/502 Base Engine, with Aluminum Heads (PN 12496963)
502 hp at 5,200 rpm, 567 ft-lbs at 4,200 rpm This is the same Gen VI short-block as the 502 HO capped off with aluminum oval-port heads (PN 12363390) sporting 110-cc chambers. Compression rises to 9.6:1 with a corresponding power gain. It has some cam in it at 224/234 degrees duration at .050-inch with .527-inch intake lift and .544-inch on the exhaust, but it’s a stump puller that really hauls a light- or medium-duty truck or mid- 1960s passenger car. It’s a great choice for a big Impala, Chevelle, or Monte Carlo. This engine is also available as a lessexpensive unassembled kit (PN 12371204).
ZZ502 Deluxe—Assembled Kit, with Aluminum Heads (PN 19201332)
502 hp at 5,200 rpm, 567 ft-lbs at 4,200 rpm Available in kit form (PN 12371171) or as a partial engine short-block (PN 12568782). The Z502 Deluxe engine is the same engine as the ZZ502 Gen VI base engine, but it is fully dressed from carburetor to oil pan. It includes an HEI distributor, spark plugs, wires, starter, water pump, crankshaft dampener, and aluminum intake manifold with an 870-cfm Holley 4-barrel carburetor. The distributor provided in this engine comes with a melonized distributor gear that is compatible with all-steel roller camshafts. This is a fully dressed plug-and-play engine suited for completing any hot street machine or street rod. You can also purchase this entire engine as an unassembled kit (PN 12371171).
Ram Jet 502 (PN 12499121)
502 hp at 5,100 rpm, 565 ft-lbs at 3,200 rpm
This sweet combination is basically the same engine as the GRN VI ZZ502, but it includes a two-piece Chevrolet Performance multi-port EFI intake manifold/plenum assembly (PN 12499249), eight sized injectors, a throttle body, and an updated MEFI 4 calibrated engine controller for plugand-play operation. The EFI intake is formidable looking at nearly 11 inches tall. It clears most truck installations, but likely requires hood modifications in many cars.
A robust bottom end supports this package with an all-forged rotating assembly and a smooth hydraulic roller camshaft. The heads are high-flow aluminum oval-port units from Chevrolet Performance.
ZZ572/620 Deluxe (PN 19201333)
620 hp at 5,500 rpm, 650 ft-lbs at 4,500 rpm
The 620-hp ZZ572 Deluxe is a fully dressed Gen VI bad-boy street engine based on a tall-deck siamesed-bore Bowtie block (PN 19212195). It has a bore of 4.560 inches, an internally balanced forged crank with a stroke of 4.375 inches, and a one-piece rear main seal. Forged aluminum pistons and forged 4340 H-beam connecting rods (.400 inch longer than stock) complete the rotating assembly.
The rectangular-port aluminum heads (PN 12499255) feature large 2.250-inch intake valves and 1.88-inch exhaust valves. The 118-cc chambers make it fully pump-gas compatible with a 9.6:1 CR. A serious hydraulic roller cam sports 254/264-degrees duration at .050- inch lift and it bumps the valves .632 inch on both the intake and the exhaust. The heads also include stud-mounted 1.7:1 aluminum roller rockers. To complete the package an 850-cfm Holley 4-barrel tops a single-plane aluminum intake manifold.
An aluminum water pump cools this monster and an HEI distributor with melonized distributor gear handles the ignition chores. It comes complete with plugs, wires, and a 14-inch flexplate, but no starter or fuel pump. You can also order this engine as the ZZ572/620 base engine (PN 12498792). It comes with a fully assembled bottom end that includes forged crankshaft, rods and pistons, and the formidable .632-inch-lift roller camshaft. The base engine is a long-block assembly that you finish off with the induction system and accessories of your choice.
ZZ572/720R Deluxe (PN 19201334)
720 hp at 6,250 rpm, 685 ft-lbs at 4,500 rpm
The R in this engine designation stands for race and this 720-hp engine packs a lot of racing performance within its 572-ci displacement. It is a serious “track only” rat motor similar to its 620- hp street sibling, but it packs a mechanical roller lifter cam with .714-inch lift and 278/282 degrees of valve duration at .050-inch lift. The CR is 12:1 and it requires 110-octane racing gas. It uses rectangular-port aluminum heads (PN 88961160) and a single-plane aluminum intake topped with a 1,150-cfm Holley Dominator carburetor. It comes complete from carburetor to pan excluding starter and fuel pump.
In addition, like the 572/620 Deluxe engine, it can be ordered as a base long-block assembly (ZZ572/720R; PN 12498826) so you can add the heads and induction system of your choice. This is a turnkey race engine capable of 9-second quarter-mile times in most Camaros, Novas, or Chevelles.
The most obstructive component compatibility issue exists between Mark IV big-blocks and the Gen V introduced in 1991. Three primary problems exist: core holes and coolant passages, rear main seals, and the loss of a fuel pump mount on the front of the block. Coolant passage revisions make Mark IV cylinder heads incompatible with later Gen V and VI cylinder blocks. Gasket manufacturers and Chevrolet revisions to Bowtie and Gen VI blocks have subsequently solved these initial stumbling blocks.
Mark IV cylinder blocks were manufactured with two- or four-bolt main caps and two-piece rear main seals, whereas all Gen V and VI blocks have four-bolt mains and one-piece rear main seals. The crankshafts are not interchangeable, but there are plenty of each available through General Motors and the aftermarket so it’s not a major issue. You simply have to match the crank to the block. All tall-deck blocks, regardless of series, have four-bolt mains, and the front four main caps on all Mark IV blocks are freely interchangeable with Gen V and VI blocks as long as the block is properly align-honed and the correct-length bolts for the caps to be used are included.
Gen V blocks do not have a fuel pump mounting boss because they were intended for use with fuel-injected engines in vehicles with in-tank electric fuel pumps. The fuel pump boss was reincorporated on Gen VI blocks to eliminate this inconvenience.
Written by John Baechtel and Posted with Permission of CarTechBooks