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GMC Big Block Chevy (1970–1972) specs: 402 ci (6.6L) 8-cylinder, 4.125 x 3.76 in (104.8 x 95.5 mm) bore and stroke. Built 1970–1972.
The GMC Big Block Chevy (1970–1972) is oversquare — the 4.125" bore exceeds the 3.76" stroke by 9.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.76" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 50.3 ci (823 cc).
It is one of 11 engines in the Big Block Chevy family, sitting between the 396 ci and 502 ci members. 2 factory variants share these dimensions across 1970–1972.
| Displacement | 402 ci / 6.6 L |
|---|---|
| Bore | 4.125" |
| Stroke | 3.76" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.5–10.25:1 (published figures vary) |
| Bore/stroke ratio | 1.097 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Years | 1970–1972 |
| Bore/stroke character | 1.097 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,760 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 50.3 ci |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1970 | — | — |
| 1972 | — | — |
1 factory vehicle, 1970–1972. Each year opens that model's engine table.