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GMC Small Block Chevy (1968–1972) specs: 307 ci (5.0L) 8-cylinder, 3.875 x 3.25 in (98.4 x 82.6 mm) bore and stroke, 9:1 compression. Rated 200 hp, 1968–1972.
The GMC Small Block Chevy (1968–1972) is oversquare — the 3.8748" bore exceeds the 3.25" stroke by 19.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.25" stroke does not reach 4,000 ft/min of mean piston speed until about 7,400 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 38.4 ci (629 cc).
9:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 27 engines in the Small Block Chevy family, sitting between the 265 ci and 400 ci members. 5 factory variants share these dimensions, rated at 200 hp across 1968–1972.
| Displacement | 307 ci / 5 L |
|---|---|
| Bore | 3.8748" |
| Stroke | 3.25" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.192 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 200 hp |
| Years | 1968–1972 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1968 | gross | 200 @ 4600 | 300 lb-ft @ 2400 | 9:1 | 310° / 320° | 0.390" / 0.410" | 112.5° |
| 1970 | gross | 200 @ 4600 | 300 lb-ft @ 2400 | 9:1 | 310° / 320° | 0.390" / 0.410" | 112.5° |
| 1971 | gross | 200 @ 4600 | 300 lb-ft @ 2400 | — | 280° / 288° | 0.390" / 0.410" | 113° |
Factory specification sheet. Durations are the factory's advertised figures at the basis printed on the sheet, not duration at .050" lift; lobe separation is calculated from the printed valve timing.
| Bore/stroke character | 1.192 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,250 ft/min — conservative for a street engine |
| Displacement per cylinder | 38.4 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| 1968 | 200 hp | — |
| 1969 | 200 hp | — |
| 1970 | 200 hp | — |
| 1971 | 200 hp | — |
| 1972 | — | — |
1 factory vehicle, 1968–1972. Each year opens that model's engine table.