General Motors Engine Prefix and Suffix Codes Explained
Small Block Chevy
: Machined pad in front of the passenger side cylinder head. Often hidden by the alterator.
Big Block Chevy
: Machined pad in front of the passenger side cylinder head or above timing chain cover.
: Passenger side of the block behind the distributor.
The prefix portion
of the ID code tells you the engine assembly plant code, and the engine’s assembly date (for example, 0701 = July 1st….no year is indicated). The suffix portion tells you the original application, vehicle model, engine RPO/ transmission / horsepower, etc… (for example, CTY = 1970 396 Camaro, 375 hp, 11.0:1, TH400).
The engine assembly date must precede the car build date (often by a few days), otherwise something is amiss. Some engine machining operations (decking) will obliterate the engine ID.
Engine ID Code Example: V0101CLJ
– (V = Plant, 01 = Month, 01 = Day, CLJ = Engine Suffix Code)
Another example: T0830CTY
– (T = Tonawanda, 08 = August, 30 = 30th day, CTY = 1970 396 Camaro, 375 hp, 11.0:1, TH400)
||St. Catherines, Ontario
||(McKinnon Industries Canada)
||GM of Mexico
Suffix codes are either alphabetical or alphanumeric. Select the portion of the alphabet for your code. For example, select “DTR-HQ” if you’d like to find code DZ. In some cases suffix codes are reused twice or more
over time, in this event check the partial VIN code or block casting date code and then see what year the block was made to pin down what application your block was originally used in.
CODE CExxxx (counter or crate engine) was used from 1968 to current year. It represents any CID and is used to indicate this particular engine was replaced under Warranty. It is a direct replacement for the original equipment. It doesn’t indicate what the original equipment was.
– is an example of a over the counter crate engine. “2800” is the last 4 digits of the GM part # for the crate engine assembly. The final digit could be a year code.
Another example: A Targetmaster engine (p/n 14009800) built in 1985 could have a code stamped as follows:
A0198005 (A = january, 01, 9800 = pn, 5 = 1985).
Small block casting date is located on driver side rear of block on flange forward of bellhousing. Big block on the right side of engine above the oil pan rails.
Casting Date Example: E038
– (E = Month, 03 = Day, 8 = Last digit of model year (1978)).
Month: A = Jan, B = Feb, C = Mar, D = Apr, E = May, F = Jun, G = July, H = Aug, I = Sep, J = Oct, K = Nov, L = Dec
On some Saginaw blocks, intakes and exhausts a “clock” was cast into the block. The clock is a circle of 10 dots, one dot for each hour of a shift (usually 10 hour shifts). An arrow points to the beginning of the shift an another dot outside the circle indicates what time of day the cast part was made. Anyways, that’s what that circle thing is (if you happen to see it on something).