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Ram Cummins ISB 24-valve specs: 359 ci (5.9L) 6-cylinder, 4.016 x 4.724 in (102 x 120 mm) bore and stroke. Rated 235 hp, 1998–2002.
The Ram Cummins ISB 24-valve 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).
It is one of 8 engines in the Cummins B Series family, all of them 359 ci — the differences between them are in compression, heads and rating, not displacement. 5 factory variants share these dimensions, rated at 235 hp across 1998–2002.
| Displacement | 359 ci / 5.9 L |
|---|---|
| Bore | 4.0157" |
| Stroke | 4.7244" |
| Cylinders | 6 |
| Configuration | I6 |
| Bore/stroke ratio | 0.85 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | diesel |
| Advertised HP | 235 hp |
| Years | 1998–2002 |
| 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 |
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These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1998 | 235 hp | Cummins ISB 24-valve |
| 1999 | 235 hp | Cummins ISB 24-valve |
| 2000 | 235 hp | Cummins ISB 24-valve |
| 2001 | 235 hp | Cummins ISB 24-valve |
| 2002 | 235 hp | Cummins ISB 24-valve |