Determining an engine’s size

August 1, 2008 | By Richard Prince


I have a small block Chevy engine that I need to rebuild but I am having trouble identifying it. The casting number at the rear of the block is 3970010. According to one book I looked at this is either a 327 or a 350 cid engine.

So my question is how can I determine which cid engine I have? The numbers on the boss at the front of the engine are 11J125580 V0104CGC. The casting numbers on the cylinder heads are 14022601. My book tells me these are from a 267 cid engine circa 1980. Is it possible someone installed these heads to boost the compression ratio?


Chevrolet engine blocks with the 3970010 casting number were very widely used from 1968-79.

OEM applications in 1968 were 327 cid engines while those built afterward were 350 cid engines.

The real key to identifying what you have is the assembly stamping in the deck just forward of the passenger side cylinder head. The assembly suffix CGC indicates that the engine was originally built as a 350 cid engine for model year 1971. It was fitted with a 2-barrel carburetor and rated at 245 horsepower, and was either coupled to a Turbo Hydra-Matic automatic transmission if it went into an El Camino or a manual transmission if it went into a police car or taxi cab. The assembly code stamping V0104 indicates that the engine was built at Chevy’s Flint engine plant on January 4th. And, finally, the partial VIN sequence 11J125580 tells us that the car this engine originally went into was a two-door sedan (“11”) built in the Janesville, Wisconsin, assembly plant (“J”) and bearing serial number 125580.

As is always the case, however, your engine may have been modified over the years to such an extent that its internal parts now bear no connection to its original internals.

The only way to know for sure what the engine is and what parts are needed for its rebuild is to take it apart to inspect and measure what lurks inside. It is doubtful that someone installed the later model heads to boost compression as they likely had the opposite effect.