Oldsmobile Oldsmobile 257ci · 3.531" × 4.375" · 6.5:1 engine specs: 257 ci (4.2L), 6-cylinder, 3.531" bore x 4.375" stroke, 6.5:1 compression.
| Displacement | 257 ci / 4.2 L |
|---|---|
| Bore | 3.531" |
| Stroke | 4.375" |
| Cylinders | 6 |
| Compression ratio | 6.5:1 |
| Rod length | 6.625" |
| Rod ratio | 1.514 |
| Bore/stroke ratio | 0.807 |
| Advertised HP | 105 hp |
|---|---|
| Years | 1949 |
| Bore/stroke character | 0.807 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,375 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.514 — short — more side loading and piston dwell at TDC, typical of stroker combinations |
| Displacement per cylinder | 42.8 ci |
| Static compression | 6.5:1 — low by modern standards, generally happy on regular pump fuel |
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Source: NHRA blueprints — nhra.net blueprints