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Ford 6.4L Power Stroke specs: 388.6 ci (6.4L) 8-cylinder, 3.87 x 4.13 in (98.3 x 104.9 mm) bore and stroke, 17.2:1 compression. Rod ratio and piston speed.
The Ford 6.4L Power Stroke is undersquare — the 4.13" stroke exceeds the 3.87" bore by 6.3% — a layout that trades peak RPM for leverage and torque low in the range. The 4.13" stroke puts mean piston speed at 4,000 ft/min around 5,800 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 48.6 ci (796 cc).
At 17.2:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
It is one of 2 engines in the 6.4 Power Stroke family, all of them 388.6 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 388.6 ci / 6.4 L |
|---|---|
| Bore | 3.87" |
| Stroke | 4.13" |
| Cylinders | 8 |
| Compression ratio | 17.2:1 |
| Bore/stroke ratio | 0.937 |
| Fuel type | diesel |
|---|
| Bore/stroke character | 0.937 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,130 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 48.6 ci |
| Static compression | 17.2:1 — high enough that pump premium or better is normally required |
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