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Cummins 6BT specs: 359 ci (5.9L) 6-cylinder, 4.016 x 4.724 in (102 x 120 mm) bore and stroke, 17:1 compression. Rated 160-175 hp. Rod ratio and piston speed.
The Cummins 5.9L 12V (6BT) is undersquare — the 4.7244" stroke exceeds the 4.0157" bore by 15.0% — a layout that trades peak RPM for leverage and torque low in the range. With a 4.7244" stroke, mean piston speed reaches 4,000 ft/min at only 5,100 RPM — the practical ceiling for a production bottom end — which is why a stroke this long makes its power low and runs out of safe revs early. Each of the 6 cylinders displaces 59.8 ci (980 cc).
At 17:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
2 factory variants share these dimensions, rated from 160 to 175 hp. Factory fitments include the Dodge Ram 2500, Dodge Ram 3500, Dodge Ram D250/D350.
| Displacement | 359 ci / 5.9 L |
|---|---|
| Bore | 4.0157" |
| Stroke | 4.7244" |
| Cylinders | 6 |
| Compression ratio | 17:1 |
| Bore/stroke ratio | 0.85 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | diesel |
| Advertised HP | 160–175 hp |
| Bore/stroke character | 0.850 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,724 ft/min — above the 4,500 ft/min mark where most production bottom ends are considered at their limit |
| Displacement per cylinder | 59.8 ci |
| Static compression | 17:1 — high enough that pump premium or better is normally required |
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 |
|---|---|---|
| — | 160 hp | 6BT |
| — | 175 hp | 6BT |