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Oldsmobile 303 specs: 303 ci (5.0L) 8-cylinder, 3.75 x 3.438 in (95.3 x 87.3 mm) bore and stroke, 8:1 compression. Rated 135 hp. Rod ratio and piston speed.
The Oldsmobile Rocket (303) is oversquare — the 3.75" bore exceeds the 3.4375" stroke by 9.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.4375" stroke puts mean piston speed at 4,000 ft/min around 7,000 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 37.9 ci (621 cc).
8:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 15 engines in the Rocket family, sitting between the 260 ci and 455 ci members. Factory fitments include the Oldsmobile 88, Oldsmobile 98.
| Displacement | 303 ci / 5 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3.4375" |
| Cylinders | 8 |
| Compression ratio | 8:1 |
| Bore/stroke ratio | 1.091 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 135 hp |
| Bore/stroke character | 1.091 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,438 ft/min — conservative for a street engine |
| Displacement per cylinder | 37.9 ci |
| Static compression | 8:1 — low by modern standards, generally happy on regular pump fuel |
| Chamber volume | 99.3 cc |
|---|---|
| Rocker ratio | 1.5:1 |
| Lifter type | hydraulic |
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