Buick 401ci specs: 4.188 x 3.64 in (106.4 x 92.5 mm) bore and stroke, shared by all 2 versions. Displacement, compression and factory ratings, plus rod ratio.
| Displacement | 401 ci |
|---|---|
| Cylinders | 8 |
| Bore | 4.188" |
| Stroke | 3.640" |
| Compression | 9.0–10.3:1 |
| Advertised power | 265–325 hp |
| Years | 1963–1966 |
| Cylinder head data | 2 of 2 engines |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| Buick 401ci · 4.188" × 3.64" · 9:1 | 401 ci | 4.188" × 3.64" | 9:1 | 265 |
| Buick 401ci · 4.188" × 3.64" · 10.25:1 | 401 ci | 4.188" × 3.64" | 10.25:1 | 280–325 |
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.