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GMC 302 specs: 302 ci (4.9L) 8-cylinder, 4.00 x 3.00 in (101.6 x 76.2 mm) bore and stroke, 11:1 compression. Rated 290 hp. OHV. Rod ratio and piston speed.
The GMC Small Block Chevy (302) is oversquare — the 4" bore exceeds the 3" stroke by 33.3% — 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 37.8 ci (619 cc).
11:1 on iron heads is high enough that pump premium or better is normally required, and iron holds heat, so it is the less forgiving side of that line.
It is one of 23 engines in the Small Block Chevy family, sitting between the 265 ci and 400 ci members. Factory fitments include the GMC Sprint (Trans Am racing homologation).
| Displacement | 302 ci / 4.9 L |
|---|---|
| Bore | 4" |
| Stroke | 3" |
| Cylinders | 8 |
| Compression ratio | 11:1 |
| Bore/stroke ratio | 1.333 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 290 hp |
| Bore/stroke character | 1.333 — 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 | 37.8 ci |
| Static compression | 11:1 — high enough that pump premium or better is normally required |
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