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Ford Flathead 239 specs: 239.4 ci (3.9L) 8-cylinder, 3.188 x 3.75 in (81 x 95.3 mm) bore and stroke. Flathead. Rod ratio and piston speed worked out.
The Ford Flathead 239 is undersquare — the 3.75" stroke exceeds the 3.1875" bore by 15.0% — 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 29.9 ci (490 cc).
It is one of 6 engines in the Flathead V8 family, the largest at 239.4 ci.
| Displacement | 239.4 ci / 3.9 L |
|---|---|
| Bore | 3.1875" |
| Stroke | 3.75" |
| Cylinders | 8 |
| Bore/stroke ratio | 0.85 |
| Valvetrain | flathead |
|---|---|
| Fuel type | gas |
| Bore/stroke character | 0.850 — 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 | 29.9 ci |
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