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Ford Flathead 221 specs: 221 ci (3.6L) 8-cylinder, 3.063 x 3.75 in (77.8 x 95.3 mm) bore and stroke. Flathead, aluminum heads. Rod ratio and piston speed.
The Ford Flathead 221 is undersquare — the 3.75" stroke exceeds the 3.0625" bore by 18.3% — a layout that trades peak RPM for leverage and torque low in the range. The 3.75" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 27.6 ci (453 cc).
It is one of 6 engines in the Flathead V8 family, the smallest at 221 ci.
| Displacement | 221 ci / 3.6 L |
|---|---|
| Bore | 3.0625" |
| Stroke | 3.75" |
| Cylinders | 8 |
| Bore/stroke ratio | 0.817 |
| Head material | aluminum |
|---|---|
| Valvetrain | flathead |
| Fuel type | gas |
| Bore/stroke character | 0.817 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,750 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 27.6 ci |
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