Bore, stroke, displacement and compression for all 5 GMC Big Block Chevy engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 396–502 ci |
|---|---|
| Cylinders | 8 |
| Bore | 4.094–4.466" |
| Stroke | 3.760–4.000" |
| Compression | 8.0–11.0:1 |
| Advertised power | 230–338 hp |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| 502 | 502 ci | 4.466" × 4" | 9.6:1 | 338 |
| 454 | 454 ci | 4.25" × 4" | 8:1 | 230 |
| 427 | 427 ci | 4.25" × 3.76" | 11:1 | 335 |
| 402 | 402 ci | 4.125" × 3.76" | 8.5:1 | 240 |
| 396 | 396 ci | 4.094" × 3.76" | 10.25:1 | 325 |
Both bore and stroke vary across the family, so these are separate castings rather than variations on one block.
Compression spans 8:1 to 11:1, so fuel requirements differ meaningfully between members — worth checking before assuming parts interchange.
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.