351C Engines by VIN Tag Engine Code
Code Engine Type Comment
H 351C-2V Generic low compression 351C, '70-74
M 351C-4V Somewhat Rare, High Compression, '70-71 only
R 351C-4V Boss Very Rare, High Compression, Solid Lifters, "Boss 351", 1971 only
R 351C-4V HO Very Rare, Low Compression, Solid Lifters, "High Output" 1972 only
Q 351C-4V CJ Rare, Low Compression, "Cobra-Jet" May 1971/, '72,
Q 351C-4V CJ Rare, Low Compression, "Cobra-Jet", 1973-74, decreased performance, see 4V section notes.
General Notes:
1) Engine code "H" was used for both 351C-2V and 351W engines, and both engine types were produced simultaneously during the 1970s. For certain car models, this means that one should lift the hood to indentify which engine type (Windsor or Cleveland) is installed in a car. Note that engine code H was also used to identify the 351M engine, which appeared in 1975.
2) The 351M engine has been left out of the above list because while related to the 351C, it was only produced after the end of the 351C production and has significant differences owing to the use of a taller engine block. The 351M, a smog-era engine, should not be confused with the 351 Cleveland.
3) All hydraulic lifter 1972 - 1974 351C engines equipped from the factory with 4-barrel carburetors are "Cobra Jet" types. '73-74 CJ engines have a few, significant internal differences from the May '71/ and 1972 351CJ engines (see notes).
4) The "M" in the 5th digit of the VIN signifies the '70-71 351C-4V, and is not a reference to the 1975 & later 351M engines. Beginning in 1975, Ford's Cleveland, Ohio plant began producing a 351 engine related to the 351C, called the 351M, where M simply stands for the term "Modified". Don't confuse the "M" in 351M with the engine code for the '70-71 351C-4V engine. The VIN code for the 351M engine is "H".
5) People sometimes refer to their cars by VIN tag engine code. For example, a '72 Mustang equipped from the factory with a 351 Cobra Jet engine is commonly referred to as a "Q-Code Mustang."
Be careful what you read on the internet. Boss 351s were produced with at least two different casting numbers, one of which is shared with 2-bolt main, non-Boss 351C engines of the era - casting number is DOAE-L. For the Boss 351, Ford drilled this 2-bolt block to accept 4-bolt main caps. Most DOAE-L blocks have 2-bolt main caps. For the 351-4V CJ engine, many websites will tell you that the block casting number is D2AE-CA. Indeed, every 351C-CJ I've seen used the D2AE-CA block, but I've also seen this same block in 2V 351C Torino station wagons, with 2 bolts on all five caps. Again, it's a case of Ford selectively drilling blocks to accept 4-bolt main caps. So if you find a D2AE-CA engine, remove the oil pan and inspect the main caps before purchasing it.
