The Modified engine family, designated 351M and 400M, was produced by Ford from 1971 through 1982. These engines are closely related to the 351 Cleveland but feature a taller deck height (1 inch taller) to accommodate a longer stroke in the 400 version. The 351M and 400M share the same block and are externally identical, differing only in bore, stroke, and crankshaft.
In F-100 trucks, the Modified engines were common in sixth-generation Dentside models (1973-1979). The 400M was particularly popular as a factory option, offering good low-end torque for truck duty. These engines have a reputation for being heavy and somewhat underpowered relative to their size, but they are durable workhorses when properly maintained.
The Modified family is often confused with the Cleveland, but the taller deck height means they use different intake manifolds and some unique components. The 400M can be stroked or fitted with Cleveland performance heads for meaningful power gains. Parts availability is decent, though not as extensive as for the Windsor family. For a period-correct Dentside restoration, the 351M or 400M is the historically accurate V8 choice.