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Ford 240 Six specs: 240 ci (3.9L) 6-cylinder, 4.00 x 3.18 in (101.6 x 80.8 mm) bore and stroke. Rated 115-150 hp, 1966–1974. Used in the Ford F-100.
The Ford 240 Six is oversquare — the 4" bore exceeds the 3.18" stroke by 25.8% — a layout that favors airflow and RPM over leverage at the crank. The 3.18" stroke does not reach 4,000 ft/min of mean piston speed until about 7,550 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 2.137 is long by production standards — less side-load on the cylinder wall and gentler piston acceleration around TDC, the geometry that tolerates high RPM. Each of the 6 cylinders displaces 40.0 ci (655 cc).
It is one of 3 engines in the Ford 240ci family, all of them 240 ci — the differences between them are in compression, heads and rating, not displacement. 7 factory variants share these dimensions, rated from 115 to 150 hp across 1966–1974.
| Displacement | 240 ci / 3.9 L |
|---|---|
| Bore | 4" |
| Stroke | 3.18" |
| Cylinders | 6 |
| Configuration | I6 |
| Rod length | 6.795" |
| Rod ratio | 2.137 |
| Bore/stroke ratio | 1.258 |
| Fuel type | gas |
|---|---|
| Advertised HP | 115–150 hp |
| Years | 1966–1974 |
| Bore/stroke character | 1.258 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,180 ft/min — conservative for a street engine |
| Rod ratio | 2.137 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 40.0 ci |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1966 | 150 hp | 240 Six |
| 1967 | 150 hp | 240 Six |
| 1970 | 150 hp | 240 Six |
| 1971 | 140 hp | 240 Six |
| 1972 | 120 hp | 240 Six |
| 1973 | 115 hp | 240 Six |
| 1974 | 115 hp | 240 Six |