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The Chevrolet big-block engine is a series of large-displacement, naturally-aspirated, 90°, overhead valve, gasoline-powered, V8 engines that was developed and have been produced by the Chevrolet Division of General Motors from the late 1950s until present.
The L78 was a Big-Block engine produced by Chevrolet between 1965 and 1970. Rated at 425 hp (317 kW) for its first year, the rating dropped to 375 hp (280 kW) in subsequent years (although there was no change in power).
The L72 was a 427 cu in (7.0 L) 90° overhead valve V8 big-block engine produced by Chevrolet between 1966 and 1969. Initially rated at 450 horsepower, the rating dropped to 425 hp (317 kW) shortly after its release (although there was no change in power).
The big-block engines initially used a forged crankshaft with a stroke of 3.975" for the 1965-1967 425 and 400 CID versions; starting in 1968, both the 400 cu in (6.6 L) and the 455 cu in (7.5 L) big blocks used a stroke of 4.25 in (108 mm), with crankshaft material changed to cast iron except in a few rare cases.
Design features of the B and RB engines include 17 capscrews per cylinder head, a cylinder block that extends 3 in (76.2 mm) below the crankshaft centerline, an intake manifold not exposed to crankcase oil on the underside, stamped-steel shaft-mounted rocker arms (race versions used forged steel rockers), and a front-mounted external oil pump driven by the camshaft.
The large increase in the main bearing size was due to replacing the forged crankshafts for all engines except the SD racing versions with the introduction of an "Armasteel" cast steel crankshaft [3]; and the engineers being very conservative in how strong the cast crankshaft would prove to be. The "Armasteel" cast crankshaft was the first cast ...
The largest engine derived from the series was a 702-cubic-inch (11.5 L) "Twin Six" V12, which had a unique block and crankshaft, but shared many exterior parts with the 351. Diesel versions of the 351, 478 and 637, advertised as the ToroFlow, were also manufactured.
This block is one of three displacements, 302/327/350, that underwent a crankshaft bearing diameter transformation for 1968 when the rod-journal size was increased from the 2 in (50.8 mm) diameter small-journal to a 2.1 in (53.3 mm) large-journal and a main-journal size that was increased from 2.3 in (58.4 mm) to 2.45 in (62.2 mm).