IN 1963, a new Chevrolet big-block set heads spinning and lips flapping when Junior Johnson blasted around Daytona Speedway at the unprecedented speed of 166 mph. The powerplant that propelled Johnson's '63 Chevy to such an incredible speed had a displacement of 427 cubic inches and was possessed of unique cylinder heads with canted valves. Such cylinder heads had never been seen before, and caused the new big-block Chevy to be tagged a "Mystery Engine."
Officially known as a Chevrolet Mark II engine, the new big-block quickly faded from sight when GM pulled its support of racing. But two years later, the Mystery Engine reappeared. It had gone through several iterations of change, as denoted by the switch from a Mark II to a Mark IV designation, and it was released in 396ci rather than 427ci form, but the lineage was unmistakable
L78: The First Corvette Big-Block
Introduced in the middle of the '65 model year, RPO L78 established a new milestone for Corvette power--425 hp (at 6,400 rpm) and 415 lb-ft of torque (at 4,000 rpm). It was the first big-block ever factory installed in a Corvette and the first Corvette engine with a rating of more than 400 hp. Its installation required another first: a special hood with functional air vents and a unique bulge in the center to clear the air cleaner. Optional side-mounted exhaust pipes were another Corvette first for that model year.
Weighing 150 pounds more than the 327, RPO L78 achieved its displacement of 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 limited production Z16 Chevelle package, of which only 201 were produced.) This engine 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 on horsepower was temporary. The engine's initial 450hp rating was subsequently reduced to 425, although the original 460-lb-ft torque rating was maintained. Except for its 4.251-inch-diameter bore and the increase in displacement that resulted from it, the L72 was virtually identical 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
With three high-capacity two-barrel Holleys serving as the induction system's focal point, RPO L71 was rated at 435 hp at 5,800 rpm and 460 lb-ft of torque at 4,000 rpm. With an 11:1 compression ratio, a mechanical lifter cam, and an aluminum intake manifold, the L71 was a tractable street engine with enough power to rivet driver and passenger to the backs of their respective seats. Like the L88, the L71 was produced from 1967 to 1969. It was the first and last Corvette engine with 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, during 1967, 1968, and 1969, so quite a few L71s have prowled the nation's streets and dragstrips. During these years, Corvettes could also be purchased with a hydraulic-lifter version rated at 400 hp. Although big-block Corvettes were produced through 1974, the passing of the L71 marked the end of an era
L88: The First Aluminum-Headed Big-Block
Talk about breaking new ground, the L88 did so literally and figuratively. Although it shared the same dimensions (4.251-inch bore, 3.76-inch stroke) as its other 427 stablemates, the L88 has become legendary for its combination of stump-pulling torque and high-flying horsepower. The engine wasn't given a horsepower rating when it was introduced in mid-year 1967, but, ultimately, engineers at Chevrolet planted their tongues firmly in their collective cheeks and proclaimed its output at 430 hp at 5,200 rpm. The issue wasn't that the rating was false, it was merely skewed. L88s undoubtedly produced something on the order of 430 hp at 5,200 rpm. But left unsaid was that it also produced approximately 500 hp at 6,400 rpm (the engine speed at which most other solid-lifter-equipped big-blocks were rated). It's also been claimed that when equipped with headers and an open exhaust, actual output was in the vicinity of 550-575 hp.
The L88 was set apart from other 427 engines by its large-port aluminum cylinder heads and 12.5:1 compression ratio. Other special equipment included a specially modified aluminum intake manifold, an 850-cfm Holley four-barrel, a mechanical lifter cam with 264 degrees of intake and 269 degrees of exhaust duration (measured at .050-inch lift), .560-inch intake and .580-inch exhaust lift, special valvesprings, a 2.19-inch intake, 1.84-inch exhaust valves, and 7/16-inch-diameter pushrods.
The L88 was a race engine. Period. However, race engines typically find their way into street-driven cars, and the L88 was no exception. But as Corvette News noted in an exercise in understatement, "The L88 is not an engine for ordinary everyday driving. It gives a rough idle, is not the easiest engine to start, and was not designed with high fuel economy in mind."
Available from 1967 through 1969, L88 Corvettes were limited-edition automobiles. (The L88 option was priced at $947.90 in 1967 and 1968, and at $1,032.15 in 1969.) Only 20 were produced the first year, 80 in 1968, and 116 in 1969. However, quite a few L88 engines were purchased over the parts counter, so there are probably now more "L88 Corvettes" in existence than were ever produced by General Motors.
ZL1: The First Aluminum Big-Block
It borders on blasphemy to talk about infamous Corvette big-blocks without including the ZL1, but this engine's impact on Corvette engine history is minimal since only two documented vehicles were ever produced. The ZL1 was simply an L88 with an aluminum block and a $4,718 price tag. Although it's considerably lighter than its cast-iron counterpart, the ZL1 didn't produce any more power. (See L88 above.)
LS6: The Last Corvette Big-Block
Although 1971 was the first year of reduced compression ratios, it was also the first year--and last--for a solid-lifter version of the 454ci (4.251-inch bore, 4-inch stroke) big-block. Wearing option RPO LS6, it was rated at 425 hp at 5,600 rpm and sported aluminum cylinder heads, a 9:1 compression ratio, an aluminum intake manifold, and an 800-cfm Holley four-barrel. Other niceties included a cross-drilled, nitrided crankshaft, domed pistons, and a $1,220.70 price tag.
In essence, the LS6 was a streetable version of the L88. The increase in stroke somewhat offset the loss of compression ratio, so all in all the LS6 was a better engine for non-racing use. And in spite of emissions regulations and all the other baggage that Detroit had to carry in the early '70s, the LS6's 425 hp (325 net) was underrated.
Some would argue that the LS7 should occupy this space, but although the engine was announced and specifications printed, the LS7 was never installed
Legendary Big-Blocks
RPO CID Horsepower Torque Carburetion
L78 396 425 @ 6,400 415 @ 4,000 Holley 4V
L72 427 425 @ 6,400 460 @ 4,000 Holley 4V
L71 427 435 @ 5,800 460 @ 4,000 3x2 Holley
L88 427 430 @ 5,200 450 @ 4,400 Holley 4V
ZL1 427 430 @ 5,200 450 @ 4,400 Holley 4V
LS6 454 425 @ 5,600 475 @ 4,000 Holley 4V
