Examining The Legendary Chevrolet Big-Block Engine

The ticking timeline to the ultimate Corvette performance engine family

Dave Emanuel Sep 22, 2005 0 Comment(s)
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The big-block Chevrolet engine had a 10-year run from 1965 to 1974,quite a feat by anyone's standards.

In 1963, a new Chevrolet big-block set heads spinning and lips flappingwhen Junior Johnson blasted around Daytona Speedway at the unprecedentedspeed of 166 mph. The powerplant that propelled Johnson's '63 Chevy tosuch an incredible speed had a displacement of 427 cubic inches and waspossessed of unique cylinder heads with canted valves. Such cylinderheads had never been seen before, and caused the new big-block Chevy tobe tagged a "Mystery Engine."

Officially known as a Chevrolet Mark II engine, the new big-blockquickly faded from sight when GM pulled its support of racing. But twoyears later, the Mystery Engine reappeared. It had gone through severaliterations of change, as denoted by the switch from a Mark II to a MarkIV designation, and it was released in 396ci rather than 427ci form, butthe lineage was unmistakable.

L78: The First Corvette Big-Block

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The '65 396/425hp engine was built only one year, but was the testbed ofthe incredible 427 powerplant to come in 1966.

Introduced in the middle of the '65 model year, RPO L78 established anew milestone for Corvette power--425 hp (at 6,400 rpm) and 415 lb-ft oftorque (at 4,000 rpm). It was the first big-block ever factory installedin a Corvette and the first Corvette engine with a rating of more than400 hp. Its installation required another first: a special hood withfunctional air vents and a unique bulge in the center to clear the aircleaner. Optional side-mounted exhaust pipes were another Corvette firstfor that model year.

Weighing 150 pounds more than the 327, RPO L78 achieved its displacementof 396 cubic inches by way of a 4.094-inch bore and 3.760-inch stroke.(A virtually identical version of the engine was rated at 375 hp,detuned with a hydraulic lift cam, and incorporated in the limitedproduction Z16 Chevelle package, of which only 201 were produced.) Thisengine featured a mechanical-lifter cam, an 11:1 compression ratio,large-port heads (with 2.19-inch intake and 1.72-inch exhaust valves),an aluminum intake manifold, and a Holley four-barrel carb.

L72: The First 425hp 427

For the '66 model year, a 425hp 427 replaced the 425hp 396. Apparently,although the increase in displacement was permanent, its effect onhorsepower was temporary. The engine's initial 450hp rating wassubsequently reduced to 425, although the original 460-lb-ft torquerating was maintained. Except for its 4.251-inch-diameter bore and theincrease in displacement that resulted from it, the L72 was virtuallyidentical to the L78. Had it not been for GM's 400ci displacement limit,the L72 would have appeared in 1965.

L71 :: The First (and only) 3x2-Barrel Corvette Engine

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In 1967, the L71 engine option was released as a 435hp monster, capableof killing just about anything on the street or strip.

With three high-capacity two-barrel Holleys serving as the inductionsystem's focal point, RPO L71 was rated at 435 hp at 5,800 rpm and 460lb-ft of torque at 4,000 rpm. With an 11:1 compression ratio, amechanical lifter cam, and an aluminum intake manifold, the L71 was atractable street engine with enough power to rivet driver and passengerto the backs of their respective seats. Like the L88, the L71 wasproduced from 1967 to 1969. It was the first and last Corvette enginewith three two-barrel carburetors and, although overshadowed by the L88,the L71 left its own performance legacy.

Production volumes were 3,754, 2,898, and 2,722, respectively, during1967, 1968, and 1969, so quite a few L71s have prowled the nation'sstreets and dragstrips. During these years, Corvettes could also bepurchased with a hydraulic-lifter version rated at 400 hp. Althoughbig-block Corvettes were produced through 1974, the passing of the L71marked the end of an era.




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