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GMC 307 specs: 307 ci (5.0L) 8-cylinder, 3.799 x 3.382 in (96.5 x 85.9 mm) bore and stroke, 8:1 compression. Rated 140 hp. OHV. Rod ratio and piston speed.
The GMC Oldsmobile V8 (307) is oversquare — the 3.7992" bore exceeds the 3.3819" stroke by 12.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.3819" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 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).
8:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 7 engines in the Oldsmobile V8 family, the smallest at 307 ci. Factory fitments include the Oldsmobile Cutlass, Buick Regal, Chevrolet Caprice and 1 other.
| Displacement | 307 ci / 5 L |
|---|---|
| Bore | 3.7992" |
| Stroke | 3.3819" |
| Cylinders | 8 |
| Compression ratio | 8:1 |
| Bore/stroke ratio | 1.123 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 140 hp |
| Bore/stroke character | 1.123 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,382 ft/min — conservative for a street engine |
| Displacement per cylinder | 38.4 ci |
| Static compression | 8:1 — low by modern standards, generally happy on regular pump fuel |
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