---
title: "Modified Engine — Ford F100 Glossary | fordf100s.com"
description: "Ford's 351M and 400M V8 family, taller-deck Cleveland-based engines used in many 1970s and early-1980s F-100s and F-150s."
canonical_url: "https://www.fordf100s.com/glossary/modified-engine/"
last_updated: "2026-09-16"
---

1. [ Home ](/)
2. / [ Glossary ](/glossary/)
3. /  Modified Engine

Glossary Term

#  Modified Engine — Ford F100 Glossary 

Ford's 351M and 400M V8 family, taller-deck Cleveland-based engines used in many 1970s and early-1980s F-100s and F-150s.

fordf100s.com · Updated September 16, 2026 

Definition

Ford's 351M and 400M V8 engines (1971-1982), related to the 351 Cleveland but with a taller deck height, commonly found in Dentside F-100s and F-150s.

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.

Related Terms

[ Cleveland ](/glossary/cleveland/)[ Windsor ](/glossary/windsor/)[ FE Engine ](/glossary/fe-engine/) 

## Keep Exploring

[PartsFord Flathead V8: Complete Specs, History & HP GuideFord Flathead V8 (1932-1953) -- displacement, horsepower by year, common problems, performance upgrades, and its role in F-100 and hot rod history.](/parts/flathead-v8-engine-guide/)[RestorationF-100 EFI Conversion: Carb to Fuel InjectionConvert your Ford F-100 from carburetor to EFI with this complete guide covering Holley Sniper, FiTech, fuel system upgrades, wiring, and tuning.](/restoration/efi-conversion-guide/)[RestorationHow to Plan an F-100 Engine SwapPlan an F-100 engine swap from measurements and mock-up through fabrication, wiring, first start, road testing, inspection, and complete build documentation.](/restoration/engine-swap-guide/)[GenerationsAll GenerationsBrowse every F100 generation](/generations/)

VIN Decoder

 Decode supported F-100 VIN formats, or use the 1961-1983 data plate decoder for source-backed paint, trim, axle, and transmission codes. 

[Decode a VIN → ](/vin-decoder/) [1961-1983 Data Plate Decoder → ](/data-plate-decoder/)