Originally posted by lvmoose007
'C's were built in the US from model year 1970 to 1974(?), and 400s from 70-71(?) to around '78(?), and 351m's from around 75 to 81-82.
keep in mind, that you are kind of limited to what you can do with the 351c, you can only modify it so far before it starts becoming more of a hi-rpm screamer, and useless for heavy truck useage. The 400 is the best to use(you can add 400 pistons and a 400 crank really easy) for heavy trucks, the 2 I built pulled like turbines from idle to 5000 rpm, and with wimpy cams......
If I remember why the 351C,M,and 400 were canceled was due to space limitations in vehicles, and Ford wanted to keep the engines (I can't think of the word, maybe platform.....) the same basic design, and the 351m and 400 were oddballs, and treated like red-headed stepchildren.
anyway that is a general idea of who and why about the 351c,M, and 400.......
I believe the 400s and 351Ms were phased out at the same time, 1982 and Ford decided to go with the 460 as the only large displacement truck engine.
Also I'm with bubba on the reasons for the demise of the 351M/400. It's the only engine which wasn't easily adaptable to a computer controlled EFI setup because the thermactor ports are in the heads instead of the exhaust manifolds so it's difficult to get an EGO reading "upstream" of the air injection ports . Even the late model Clevelands had thermactor ports cast into the heads.