Bore, stroke, displacement and compression for all 2 Buick Nailhead V8 engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 401–425 ci |
|---|---|
| Cylinders | 8 |
| Bore | 4.188–4.313" |
| Stroke | 3.640" |
| Compression | 10.3:1 |
| Advertised power | 325–340 hp |
| Cylinder head data | 1 of 2 engines |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| 425 | 425 ci | 4.3125" × 3.64" | 10.25:1 | 340 |
| 401 | 401 ci | 4.1875" × 3.64" | 10.25:1 | 325 |
Stroke is constant at 3.64" across the family — the displacement spread comes from bore, so these share a crank and differ in the block.
All are oversquare — bore larger than stroke, which favours revs over low-end torque.
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.