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Oldsmobile 257ci (1941–1948) specs: 257 ci 8-cylinder, 3.25 x 3.875 in (82.6 x 98.4 mm) bore and stroke, 6.5:1 compression. Rated 110 hp, 1941–1948.
The Oldsmobile 257ci (1941–1948) is undersquare — the 3.875" stroke exceeds the 3.25" bore by 16.1% — a layout that trades peak RPM for leverage and torque low in the range. The 3.875" stroke puts mean piston speed at 4,000 ft/min around 6,200 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 32.1 ci (526 cc).
6.5:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 2 engines in the Oldsmobile 257ci family, all of them 257 ci — the differences between them are in compression, heads and rating, not displacement. 5 factory variants share these dimensions, rated at 110 hp across 1941–1948.
| Displacement | 257 ci |
|---|---|
| Bore | 3.25" |
| Stroke | 3.875" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 6.5:1 |
| Bore/stroke ratio | 0.839 |
| Fuel type | gas |
|---|---|
| Advertised HP | 110 hp |
| Years | 1941–1948 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1946 | gross | 110 @ 3600 | 210 lb-ft @ 2000 | 6.5:1 | 215° / 235° | 0.300" | 107.5° |
Factory specification sheet. Durations are the factory's advertised figures at the basis printed on the sheet, not duration at .050" lift; lobe separation is calculated from the printed valve timing.
| Bore/stroke character | 0.839 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,875 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 32.1 ci |
| Static compression | 6.5:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1941 | — | — |
| 1942 | 110 hp | — |
| 1946 | 110 hp | — |
| 1947 | 110 hp | — |
| 1948 | — | — |
1 factory vehicle, 1941–1948. Each year opens that model's engine table.