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GMC 265 specs: 265 ci (4.3L) 8-cylinder, 3.75 x 3.00 in (95.3 x 76.2 mm) bore and stroke, 8:1 compression. Rated 162 hp. OHV. Rod ratio and piston speed.
The GMC Small Block Chevy (265) is oversquare — the 3.75" bore exceeds the 3" stroke by 25.0% — a layout that favors airflow and RPM over leverage at the crank. The 3" stroke does not reach 4,000 ft/min of mean piston speed until about 8,000 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 33.1 ci (543 cc).
8:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 23 engines in the Small Block Chevy family, the smallest at 265 ci. Factory fitments include the GMC 100 Series, GMC Suburban.
| Displacement | 265 ci / 4.3 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3" |
| Cylinders | 8 |
| Compression ratio | 8:1 |
| Bore/stroke ratio | 1.25 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 162 hp |
| Bore/stroke character | 1.250 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,000 ft/min — conservative for a street engine |
| Displacement per cylinder | 33.1 ci |
| Static compression | 8:1 — low by modern standards, generally happy on regular pump fuel |
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