How to Identify Chevy Bowtie Blocks

by Floyd Drake III
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Chevrolet Bowtie engine blocks are special-order engine blocks manufactured by the GM High Performance division. Bowtie blocks are used for racing, including NASCAR, and other high-performance applications. Available in both big and small block displacements, Bowtie blocks are manufactured with high tolerances and special machining, enabling them to withstand 600 horsepower or more. Chevrolet offers a full line of Bowtie blocks, each designed for a different purpose with individual specifications. Identifying Bowtie engine blocks requires you to locate both the bowtie casting mark and the block casting number.

Step 1

Locate the Bowtie casting mark. The Bowtie casting mark is found on the side of the engine block, between the side of the cylinder head and the oil pan, or on the side of the block, in the center of the oil pan rail. Only Chevrolet Bowtie blocks have the bowtie casting mark. Some blocks are mirrored, with the bowtie located in the same location on each side of the block.

Step 2

Find the engine block casting number. Located on the top rear of the engine block behind the intake manifold, the casting number is between six and eight digits long; for example, 366286.

Step 3

Reference the block casting number to identify the Chevrolet Bowtie block. When referenced to the listing found on the Chevy Legends site, casting number 366286 identifies a Bowtie engine block with a four-bolt main bearing, 4.00- to 4.150-inch cylinder bores and a 2.45-inch main journal. Both the Chevy Legends and Joe's Antique Auto sites list casting numbers for Chevrolet small-block engines, while Fastnuf has a Chevrolet big-block casting number listing (see Resources).

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