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| Making its production debut in 1965, Chevy's 396 cubic-inch Mk. IV big block came in two flavors: 375-horse in the Z-16 Chevelle, and 425-horse for Corvettes and Impalas. |
The 425-horse 396, M-22 4-speed and 4.88-geared 12-bolt Posi meant bigperformance in this '65 Impala Super Sport. |
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| Continue from Chevrolet pt.2 |
The Mark IV production version of the Mystery Motor was unveiled in 1965. Initially available in only two forms, 375-horse (destined for the Z-16 Chevelle) and 425-horse (Corvette, Impala) versions, both of which displaced 396 cubic inches. In 1966, with Mark IV production in full swing, the standard-performance versions making 325 horsepower became available on models across the board.
The big news in ‘66, though, was the new 427 cubic inch version of the Mark IV. Available in the Corvette and Impala lines, the 427 came in two horsepower levels: 390 and 425. The 390-horse engines had hydraulic cams, while the 425-horse versions used the same camshaft as the 396-425 engine of ‘65.
1967 saw the release of two truly special big blocks: the L-88 and L-71 427s. The L-88 engine was basically a race engine built only in sufficient quantities to satisfy the homologation rules of various racing sanctioning bodies. These engines featured either cast-iron or aluminum heads (aluminum heads were optional) and a healthy 12.5:1 compression ratio. Specifications for the mechanical camshaft were .562” intake, .584” exhaust lift; 354° intake and 360° exhaust duration. The bottom end was of course all forged with 4-bolt main bearing caps. Although no horsepower figures for the L-88 were released by Chevrolet in 1967, they arbitrarily tagged the virtually identical 1968 version at 430. True figures were probably in the 500 range.
The other special 427 for 1967 was the L-71. This engine, while more tame than the L-88 competition powerplant, was nevertheless rated 5 horsepower higher at 435. (This should tell you something about the factory ratings on special engines.) Featuring three Holley 2-bbls on an aluminum intake manifold covered by a unique triangular air cleaner, the L-71 made quite a visual impression when a lucky owner popped the hood on his Corvette. L-71 compression was a more livable 11.25:1, with the standard for high-performance big blocks 2.19” and 1.72” valves. The mechanical cam specs were .520” lift int/exh, 316° intake and 302° exhaust duration. Aluminum heads were made available as an option (RPO code L-89) on both L-88 and L-71 engines, the first use of aluminum as a production head material by Chevrolet. It should be noted that while the L-71 Tri-Carb 427 was readily available to the general public in production Corvettes, the L-88 was much more restricted in its availability. (Next Page) |
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| Installation in a wide variety of models made the 396 a legendary muscle car powerplant. |
Through the mysterious C.O.P.O.program, Camaros and Chevellescould be had with 427 power. |
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