The legend began on the high banks of Daytona in February 1963. A handful of Chevrolets arrived for the Daytona 500 with something "mysterious" under the hood. While Ford and Chrysler expected to compete against Chevrolet's venerable "W" head 409, the Bow-Tie guys had a rather large surprise waiting for them. As Junior Johnson's Chevy thundered around the track at speeds in excess of 160 mph, every soul from the garages, to the pits, to the stands knew that was no W block. Hot on Junior's heels was Johnny Rutherford in another Chevy. The Chevrolets of Ray Fox, Smokey Yunick, and Bubber Farr all ran with power unmatched by the 409, and Ford and Chrysler cried foul. What was this "mystery motor" that Chevrolet was running?
Inside Chevrolet Engineering, it was called the Mark II, a 427ci V-8 that had no bloodline with the 409, which was dubbed the "Mark I." The word "Mark" was derived from the European tradition of using "Mark" to designate succeeding phases of a design. Instead, it was a totally new design that started in the summer of 1962 when Chevrolet Engineering's Dick Keinath started work on a replacement for the W block. Keinath started with the same bore centers (4.84-inch) as the W block. To keep things differentiated in the minds of Chevy engineers working on both engines, the planned successor to the W block was dubbed "Mark II." It was this big-bore, short-stroke 427 powerhouse that tore up the Daytona high banks.
The Mark III was a 1963 design study that had features like the Mark II, but had a bigger bore center. None were produced, since it required too much tooling money at the Tonawanda engine plant to change bore centers. The Mark IV went into production in 1965, displacing 396 ci. Mark IVs were subsequently produced in versions of 427 and 454 cid. Deck heights were 9.80 inches
The cylinder heads were kept under wraps at Daytona in 1963, and all throughout the development process. Less than 50 of these engines had been cast before GM slipped out of racing in January 1963. The large-diameter valves were canted, causing them to stick out at odd angles, which then lead to the engine being nicknamed "Porcupine."
From 1965 until it was discontinued in 1974, the Mark IV big-block was produced in a variety of horsepower configurations. It served duty in everything from mundane station wagons with trailer packages, to pavement-melting super Chevys that ruled the streets and the drags.
Even after they were discontinued from production, the Chevy big-block continued on as the GEN II crate motor that powers drag cars, street rods, and the hottest street machines today. Like all great engines, the Chevy big-block will be around to power street machines for generations to come.
The Mark IV 396ci V-8 was introduced in 1965, and was available in the Corvette and the full-sized Chevrolet. With the valve cover removed, the staggered arrangement of the valves is clearly visible. Header-like exhaust manifolds were extremely efficient.
The '67 L34 396ci V-8 was optional on the Chevelle and Camaro. It was rated at 350 hp. Performance versions of the 396 used an open-element air cleaner.
The '66 L72 427 was offered in both the big Chevrolet and the Corvette. The L72 produced 425 hp, and utilized big 2.190-inch intake and 1.720-inch exhausts. The '66 L35 used smaller 2.065-inch intake valves and produced 390 hp.
One of the most famous big-blocks is the '67 L71. This 427 was rated at 425 hp, and a thumpin' 460 lb-ft of torque. A trio of Holley two-barrel carburetors drew air through a triangular-shaped air cleaner with a low-restriction polyurethane element.
The King Kong of the Mark IV family was the '67-'69 L88. It differed very little from the '69 all-aluminum ZL1 shown here. The major difference was that the L88 used an iron block. Both engines were ridiculously underrated at 430 hp, and were true race engines. Chevrolet sold just 216 L88-equipped Corvettes between 1967 and 1969. Only two ZL1s were installed at the factory in '69 Corvettes. A total of 69 ZL1s were installed in '69 Camaros under special Central Office orders. The ZL1 had a 12:1 compression ratio and used an alloy aluminum block with dry cylinder sleeves. Aside from that major difference, it and the L88 were virtually the same. Both used mechanical lifters and 1.70:1 rockers. The ZL1 and the L88 both used 2.185-inch intake and 1.875-inch exhaust valves made of alloy steel. The intake valve face and head was aluminized, while only the exhaust valve's face was aluminized. The L88 had 0.5500 lash at zero lift while the ZL1 had 0.5800 lift at zero lash.
In 1970, the Mark IV was treated to a 0.24-inch bore job, taking it out to 4.00. With the 4.25 stroke unchanged, the new engine displaced 454 ci. The LS5 version produced 390 hp with a hydraulic valvetrain. It was also stymied by emission control equipment.
This is the engine that never was, at least in production form. It's the LS7, and it was destined for the '70 Corvette. None were ever installed at the St. Louis assembly plant. The 460hp LS7 in this factory photo shows a trio of Holley two-barrel carburetors. Factory specifications, however, indicate that a Holley four-barrel was planned, along with aluminum heads, 11.25:1 compression, a mechanical valvetrain, and a transistorized ignition.
The ZZ502/502 is one of GM's most popular crate engines. It features a complete roller-rocker valvetrain, big-valve aluminum heads, and a dyno-tuned induction and ignition system. It's lightweight, and can be ordered as a long-block or a complete engine kit.
The "King of the Crate Engines" is the new ZZ572/620 that's built around an all-new Gen VI tall deck Bow-Tie big-block. This all-new engine is filled with a forged 4340 steel crank with 4.375-inch stroke, shot-peened, forged 4340 H-beam rods, and forged-aluminum pistons with full-floating wristpins. The 572 makes 620 hp at 5,500 rpm, and 650 lb-ft of torque at 4,500 rpm.
1965-1974 Chevrolet Mark IV Engine Specifications