GMC Detroit Diesel I6 (Two-Stroke) specs: 4.25 x 5.00 in (108 x 127 mm) bore and stroke, shared by all 2 versions.
| Displacement | 284–426 ci |
|---|---|
| Cylinders | 4, 6 |
| Bore | 4.250" |
| Stroke | 5.000" |
| Compression | 18.7:1 |
| Advertised power | 140–238 hp |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| 6-71 | 426 ci | 4.25" × 5" | 18.7:1 | 238 |
| 4-71 | 284 ci | 4.25" × 5" | 18.7:1 | 140 |
All are undersquare — stroke larger than bore, favouring torque low in the range.
Each engine page carries rod ratio, mean piston speed, bore/stroke character and cylinder head specs where published, and links into the calculators with its dimensions already filled in.