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How to Tell the Difference Between a Chevy 427 & a Chevy 454

by Richard Rowe

Chevy enthusiasts have a saying: "There are only two kinds of people: those who have a big block and those who want one." While far heavier and more complex than the small block, Chevy's iron dinosaur carries a mystique that only a few of its smaller cousins can match. While the 396 was undoubtedly more common, the 454 and 427 big blocks provide far superior levels of power potential and cachet.

Look at the valve covers. Chevrolet produced two generations of big-block engine: the earlier "W" series big block and the second-generation MkIV series. Produced from 1958 to 1965, the first generation got its nickname from its W-shaped valve covers. This generation includes the 348, 409 and 427; the 454 was an MkIV engine with rectangular valve covers. If you see W-shaped (or M-shaped, depending on your perspective) valve covers, it's not a 454.

Locate the casting number on the back of the block, which you can find cast into the driver or passenger side top of the bell housing ridge --- the the 2-inch-wide flange on the back of the block where the transmission bolts to the engine. You may need to use a hand mirror and flashlight to locate it and will probably need to clean it with some carburetor cleaner and a rag to read it.

Note the number. Chevy's 427 engines used several different casting numbers, depending on design and application: 340220 (1968 through 1976), 364776 (1974 through 1976), 473478 (1977 through 1990), 3969858 (1968 through 1973), 3999294 (1968 through 1973) and 10114184 (1991 through 1992). Numbers 3869942, 390435 and 3916321 indicate 1966, 1967 and 1968 blocks, respectively. The number 3935439 indicates a 427 short-deck motor made from 1986-1969. The 454 engine's casting numbers include 364776 (1977 through 1990), 3963512 (1968 through 1971 two- or four-bolt main), 3969854 (1972 two-bolt main), 3999289 (1972 through 1979 two-bolt main), 10114182 (1992 four-bolt main) and 14015445 (1978 through 1987 two- or four-bolt main).

Remove either one of the valve covers, and look on the cylinder head surface between the first and second set of valve springs for the head casting number. Casting numbers 3873858 (1966 through 1967), 3904391(1967 only), 3919840 (1967 through 1969) and 3919842 (1968 through 1969) could indicate either 396 or 427. Casting number 3904392 denotes it as a 1967-only 427, and number 3964291 marks a 1969-through-1970 396/402/427. The 1969-through-1971 396, 402, 427 and 454 shared the casting number 3946074. Casting numbers marking only 454 engines include 3964292, 3994025, 3994026, 6258723, 6272990, 10045427 (Chevy/Pontiac aluminum race heads), 10051128, 12363401 (Bowtie aluminum race heads), 14011077, 14044861, 14096188 and 14097088 (includes Chevrolet 502).

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About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

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