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Ford 6 9 specs: 420.2 ci (6.9L) 8-cylinder, 4.00 x 4.18 in (101.6 x 106.2 mm) bore and stroke. Used in the Ford F-250. Rod ratio and piston speed worked out.
The Ford IDI Diesel V8 (6 9) is close to square: 4" bore against 4.18" stroke, within 4.3%, which splits the difference between a high-revving layout and a torque layout. The 4.18" stroke puts mean piston speed at 4,000 ft/min around 5,750 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 52.5 ci (861 cc).
It is one of 7 engines in the IDI Diesel V8 family, the smallest at 420.2 ci.
| Displacement | 420.2 ci / 6.9 L |
|---|---|
| Bore | 4" |
| Stroke | 4.18" |
| Cylinders | 8 |
| Compression ratio | 20.7–21.5:1 (published figures vary) |
| Bore/stroke ratio | 0.957 |
| Fuel type | diesel |
|---|
| Bore/stroke character | 0.957 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 4,180 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 52.5 ci |
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1 factory vehicle, 1983–1987. Each year opens that model's engine table.