All of the 351C and 351M/400 engines differ from the 302/351W by having an integrated timing cover casting in the front of the block to which the radiator hose connects. Hcode The majority of 351 Cleveland engines are Hcode 2V (2venturi carburetor) versions with low compression.
Technical Articles: 351M/400 Performance Build Up. by Paul Eschenbach. ... the best thing you can do to your engine is to raise the compression ratio. ... ") is milled, or shaved, off of the bottom of the heads so that they will lay perfectly flat on the engine block. Shaving " will increase the compression ratio by approximately %