Mark IV Big Block Chevy Engine - The Mark of Chevy Power

Where Chevy Muscle Really Lives

Paul Zazarine Nov 1, 2006 0 Comment(s)
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"Porky" Pine rides atop the Mark IV '65 Corvette L78.

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.

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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.

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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.

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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.

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