Bore, stroke, displacement and compression for all 13 Pontiac V8 engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 326–455 ci |
|---|---|
| Cylinders | 8 |
| Bore | 3.811–4.189" |
| Stroke | 3.563–4.209" |
| Compression | 8.0–10.8:1 |
| Advertised power | 250–405 hp |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| 455 | 455 ci | 4.1496" × 4.2087" | 8.4:1 | 310–335 |
| 455 | 455 ci | 4.189" × 4.063" | 8:1 | 325 |
| 428 | 428 ci | 4.1181" × 4" | 10.75:1 | 390 |
| 428 | 428 ci | 4.189" × 3.9016" | 10.5:1 | 375 |
| 421 | 421 ci | 4.0906" × 4" | 10.75:1 | 376–405 |
| 421 | 421 ci | 4.189" × 3.811" | 10.75:1 | 370 |
| 400 | 400 ci | 4.1181" × 3.752" | 10.5:1 | 370 |
| 400 | 400 ci | 4.12" × 3.75" | 10.75:1 | 360 |
| 400 | 400 ci | 4.122" × 3.752" | 10.75:1 | 366 |
| 389 | 389 ci | 4.063" × 3.752" | 10.25:1 | 325 |
| 389 | 389 ci | 4.063" × 3.752" | 10.5:1 | 303 |
| 350 | 350 ci | 3.874" × 3.689" | 9.2:1 | 265 |
| 326 | 326 ci | 3.811" × 3.563" | 8.6:1 | 250 |
Both bore and stroke vary across the family, so these are separate castings rather than variations on one block.
Compression spans 8:1 to 10.75:1, so fuel requirements differ meaningfully between members — worth checking before assuming parts interchange.
9 of 13 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.