How to Decode Chevy Small Blocks



Deciphering Chevy’s engine casting numbers, date codes, and suffix stampings will assist you in determining exactly what you have in your new project car. These codes are also useful to have on hand when shopping at a swap meet or salvage yard. It’s not always easy to tell what you’re looking at visually, as parts from one year to the next can easily be swapped or find their way under the hoods of other models or model years. Do you want to know what you have?

What Is the Distinction Between a Casting Number and an Engine ID Code?

Casting Number for a Small Block Chevy

On Chevy small blocks there are two very important sets of numbers that can help you determine not only the displacement and horsepower level but also the original assembly line application and more. The casting number and engine ID code are represented by these two numbers. The casting number, as the name implies, is cast into the block when the block is cast. This casting number will denote engine displacement, 2 or 4 bolt main caps, application year or year range, and often any specific application notes. These casting numbers are well known and documented on several well-known websites, including Mortes, as well as in numerous Chevy ID codebooks.

How to Decode Chevy Small Blocks

ID Code for a Chevy Small Block Engine

The Chevrolet Engine ID Code Has a Prefix and Suffix Code That Provides Important Engine Specs

The engine ID code, on the other hand, is a stamping into a machined pad rather than a raised part of the casting. The prefix code and the suffix code will be included in this stamping. The suffix code will provide the original assembly line application, horsepower, and much more, so this is where the nitty-gritty details can be verified. These codes are typically alpha or alpha-numeric in nature and can be two or three characters long. The Lime Book, which covers all GM V-8 engines from 1955 to 1991, is one of the most comprehensive suffix code collections we’ve found. Early blocks will only have the ID code, whereas later engines will also have a partial VIN stamped with the ID code, as shown in this example from a 1972 Corvette with a 350 small block and a TH400 transmission.


Where Can I Find Chevy Small Block Casting Numbers?

The casting number on a small block Chevrolet is located at the rear of the block on the driver’s side. The engine ID code is stamped on a flat pad in front of the passenger cylinder head (big blocks can be in the same location or above the timing chain cover, with inline sixes stamped on the passenger side of the block behind the distributor). The alternator can sometimes obscure the engine ID code. All engines have an ID number that includes the plant code, assembly date, and suffix code. As previously stated, the suffix indicates the application, original model, engine RPO, horsepower rating, and transmission originally mated to the engine. We’ll break down the ID code prefix and suffix sections below.


This block is stamped with the GM Goodwrench 350 Crate Engine Casting Number.

There have been some changes to the standard block casting numbers and engine ID codes over the last 50 years. For example, because there was no original application for service blocks and crate engines, you won’t usually get a full engine ID. Typically, a “CE” denotes a Chevy Engine. Crate engines, for example, will frequently use an M-code “Hecho En Mexico” casting. While the engine ID on a service block or crate engine may not always tell the whole story, the casting number will. This casting number denotes a 350 cubic inch Goodwrench crate engine with a 2-piece rear main seal in our example. Later blocks will frequently have the displacement in liters cast in along with the casting number. It is common to see “5.0L” or “5.7L” on these later blocks.


SBC Engine ID Code Stamping Numbers: How Do You Decipher Them?

Let’s make up a fictitious Chevy engine ID code and then decode it using Chevy engine decoder tables. Aside from the previously mentioned Mortes site and The Lime Book resources, the site is just one of several great sites we’ve used over the years for decoding information.


V0801CML is the engine ID code.

Chevrolet Engine Plant Codes

The first letter of the stamp indicates the location of the engine’s assembly. In this case, the letter “V” stands for Flint, Michigan. The numbers after that represent the actual assembly date. The numeric code for the day and month is represented by these four digits. In this fictitious example, the engine’s assembly date is August 1st (08 for August and 01 for the day of the month). This will not be the same as the casting date for the block, more on the casting dates below. The suffix code is indicated by the letters “CML.”


The suffix codes essentially tell you what the engine was installed in on the assembly line when it was first installed. This suffix code is one of the thousands available, and it shows four possible applications, ranging from a 1975 Camaro with 155HP to a 1980 Z-28 with 190HP. The correct code can usually be determined (they have been reused over time) by decoding the partial VIN for the model year and/or the casting date found on the back of the block adjacent to the block casting number. The date will be printed on the passenger side of late-model small blocks and early big blocks. A small number of early small blocks may even have the casting date printed on the left side of the block casting.


GM VINs indicate the model year as the first character in 1960-1965 VINs, and as the sixth character in 1966-1980 VINs. For the last year of a decade, this will be denoted by a single digit (1966=6, and so on).

A Chevy Small Block Casting Date Code from the 1950s

Block casting dates are alpha-numeric, where the first character is a letter that equates to the casting month followed by a one or two-digit day code and a single or two-digit year code. If the year code is a single digit, you must confirm the decade using other block identification codes.


  1. A=January
  2. B=February
  3. C=March
  4. D=April
  5. E=May
  6. F=June
  7. G=July
  8. H=August
  9. I=September
  10. J=October
  11. K=November
  12. L=December