The History of the Chevy 402 Engineby Anne Davis
In 1963, Chevrolet unveiled the start of what would be its big block engine family: a 427-cubic-inch V8 engine. This performance engine family was eventually expanded, adding larger and smaller versions. From 1965 until 1974, Chevrolet's big blocks were called Mark IVs; among these was a 6.6-liter, also known as the 402.
The 402 had three different production codes throughout its life: LS3, L34, and L78. The L34 and L78 were manufactured only in 1970, and, except for a slightly larger bore, were identical to the equivalent versions of the 396-cubic-inch V8s with the same production codes. The LS3 was available in 1971 and 1972, and had no equivalent 396-cubic-inch V8 version.
This engine had a bore of 4.124 inches and a stroke of 3.76 inches; to compare, the 396 had a bore of 3.094 inches. The L34 had a compression ratio of 10.25-to-one and the L78 had a compression ratio of 11-to-one. The LS3 had a compression ratio of 10.25-to-one in 1971 and 8.5-to-one in 1972.
In 1970, the L34 variant of the 402 could produce 350 horsepower at 5,200 rpm and 415 ft-lb. of torque at 3,400 rpm; these are identical performance ratings as the equivalent variant of the 396. That same year, the L98 variant of the 402 was rated to produce 375 horsepower at 5,600 rpm and 415 ft-lb. of torque at 3,600 rpm.
In 1971, the LS3 produced 300 rpm at 4,800 rpm and 400 ft-lb. of torque at 3,200 rpm. In the last year of its production, 1972, the LS3 variant of this engine produced 240 horsepower at 4,400 rpm and 345 ft-lb. of torque at 3,200 rpm.
During its lifetime, this 6.6-liter V8 was used in such vehicles as the Camaro, Chevelle, Nova, and Monte Carlo. Although it displaced 6-cubic-inches more than the 396 and had a bore that was 0.03 inches wider than the 396, Chevrolet marketed the 402 as a 396 on its smaller cars like the Nova, while labeling it as a 402 in its full-size automobiles.
In this 6.6-liter engine, the cylinder head bolts to the engine block with 80 ft-lb. of torque. The four-bolt main bearing caps of the crank require 105 ft-lb. and the two-bolt main bearing caps require 95 ft-lb. of torque to attach with the block. The oil pan bolts to the engine block with 11.25 ft-lb. of torque, and its drain plug bolts to it with 20 ft-lb. The exhaust manifold and cylinder head join together with 20 ft-lb. of torque and the intake manifold and cylinder head join with 30 ft-lb.
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