FACT or FICTION? Chevy's Big Block Engine

FACT or FICTION?

Chevrolet’s legendary big block engine, like all legends, carries plenty of myths that require regular debunking to ensure rumor control. When it debuted in 1965, neatly tucked between the fiberglass wells of the Corvette, what was named the Mark IV powerplant carried a total displacement of 396 cubic inches and generated a factory-rated 425 horsepower. While the 50 more horsepower it generated over the fuel injected small-block it replaced supposedly negated the additional weight of the big block, the most impressive component was the monstrous torque increase. After all, it’s torque that really gets you down the road and drivers of these first big blocks can attest to that first hand.

Until 1975, when it was last offered as a passenger car powerplant as a much weaker, smog-reducing and fuel-squeezing counterpart from its earlier highly temperamental personality, the big block was released in many incarnations with a plethora of modifications that gave it a multitude of personalities.

Different cylinder head configurations yielded different compression ratios and an equal number of different intake and exhaust systems. Various hydraulic and mechanical camshaft profiles were utilized along with different rod bolt sizing, crank-shaft materials, and main bearing cap designs. Different block deck heights provided an engine to fit varying applications – from the bruiser musclecars and Corvettes, to a host of medium duty commercial vehicles and watercraft.

Hopefully we can dispel a few misconceptions, so read on and see if we can add a little insight with regard to the myths surrounding Chevrolet’s venerable big block. Sorry if we change your way of thinking about some of these particulars, but just remember, we’re here to help.

 

MYTH: All big-block camshafts will work in any model year big-block engine.

FALSE: The original 1965 396ci big block had a slightly different oiling system from what was to be offered in 1966. All 1965 big blocks require a special camshaft with a grooved rear main journal. Without this modification, he engine will not oil properly causing starvation and damage. Subsequent models incorporated the oiling requirement in the block and used a rear bearing with a groove in it.

MYTH: Approximately 1000 l88 corvettes were built during the years of 1967-1969.

FALSE: Only 216 cars came from the factory with the L88 engine option. Although rated at 430 horsepower, the actual horsepower rating for the engine was much higher, by some estimates as much as 560 horsepower. With 12.5:1 compression pistons, aluminum heads high-lift mechanical camshaft and a high-flow intake with four-barrel carburetor,  these were race engines, only offered to the public to homologate the engine for competition. In terms of final totals, there were 20 L88-equipped cars built in 1967, 80 in 1968 and 116 in 1969.

MYTH: The L89 aluminum cylinder head engine option was much more popular than the L88 engine option.

TRUE: While the L89 option was a great idea, it is widely believed that in 1967 only 16 cars were equipped with the L89 aluminum heads, four less than the total for the same year for L88-equipped cars with 20. However, overall there were more L89s throughout the course of its life, with an estimated 624 installed in Corvettes and as many as 400 plugged in beneath the hood of the Chevelle.

MYTH: All big-block valve covers are the same except for coloration.

FALSE: While coloration did change to include many different designs, from painted orange to chrome valve covers, the key disparity was the “drippers” that were tack welded to the inside of the valve covers. These drippers directed oil onto the top of the rocker arm stud to increase oiling. This was used only on the high performance engines and could be spotted by the slight dimpling of the exterior surface of the of the valve cover.

MYTH: Although the Chevrolet Chevelle could be ordered with the 450 horsepower ls6 454ci engine option, the same engine was not offered in corvette at anytime.

TRUE: The 450-horse LS6 engine wasn’t available as an option in the 1970 Corvette as the only 454ci engine offered was the 390 horsepower LS5 version. A few Tech Center prototypes were created with the bigger LS6 engine but corporate orders kept them from ever being released to the public. However, in 1971 a detuned LS6 producing 425 horsepower was available on the Vette’s option sheet.

About the author

PPN Editor

Power & Performance News is the source for news, tech and products that help you get more performance from your vehicle. If powertrain performance projects and hardcore technical content are your interest, Power & Performance News is the publication designed for you. Our acclaimed editorial staff covers all aspects of engine and driveline upgrades with a mission of presenting information that is both interesting and achievable for the “average car guy”.
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