How to Identify a GM Block

by Floyd Drake III

General Motors uses a systematic engine identification system that requires consulting a Chevrolet engine ID number listing. The information provided is useful, but a problem with Chevrolet engine identification is that many blocks were used for similar engines of different displacement. Cross-referencing casting numbers from other engine components can also be misleading as many of these parts were interchangeable with other engines. All this aside, the GM/Chevrolet system will tell you the vehicle the engine was intended, the year and horsepower as well as other technical identification information.

Locate the engine ID number. On small-block V8s, it is located on the passenger-side front of the engine block, right below the cylinder head. Big Block V8s normally have the number in the front, near the timing chain cover and in-line six-cylinders locate it on the passenger side behind the distributor. V6 engines generally follow the small-block V8 pattern.

Decode the ID number prefix. The prefix is five-digits long and begins with a letter. The letter refers to the engine manufacturing plant and the following four numbers indicate the month and day of manufacture. For an engine manufactured on 2 January, the number will read "0102."

Cross-reference the engine ID number with a Chevrolet engine ID listing. According to Nasty Z28, the two to three-letter suffix of the ID contains the engine identification specifics. The suffix "CEK" translates as a 1978 305 c.i.d. used in a full-size Impala, an automatic transmission and 145 horsepower. It also gives general Vehicle Identification Number references.


  • If difficulty in identifying engine ID numbers arise, contact a Chevrolet parts department. They can readily decode the number for you.

About the Author

A native of New Haven, Conn., Floyd Drake III began writing in 1984. His work has appeared in the "New Haven Register," Medford's "Mail-Tribune" and the "Ashland Daily Tidings." Drake studied journalism at Southern Connecticut State University. After working as a reporter in Oregon, he is now based back home in New Haven.

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