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Oldsmobile 371ci specs: 371 ci (6.1L) 8-cylinder, 4.00 x 3.688 in (101.6 x 93.7 mm) bore and stroke, 10:1 compression. Rated 265-312 hp, 1957–1958.
The Oldsmobile 371ci is oversquare — the 4" bore exceeds the 3.688" stroke by 8.5% — a layout that favors airflow and RPM over leverage at the crank. The 3.688" stroke puts mean piston speed at 4,000 ft/min around 6,500 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.898 is long by production standards — less side-load on the cylinder wall and gentler piston acceleration around TDC, the geometry that tolerates high RPM. Each of the 8 cylinders displaces 46.4 ci (760 cc).
10:1 is in the range that usually runs on pump premium.
It is one of 4 engines in the Oldsmobile 371ci family, all of them 371 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated from 265 to 312 hp across 1957–1958.
| Displacement | 371 ci / 6.1 L |
|---|---|
| Bore | 4" |
| Stroke | 3.688" |
| Cylinders | 8 |
| Compression ratio | 10:1 |
| Rod length | 7" |
| Rod ratio | 1.898 |
| Bore/stroke ratio | 1.085 |
| Piston deck clearance | 0.002" |
| Induction | 1-2 |
|---|---|
| Advertised HP | 265–312 hp |
| Years | 1957–1958 |
| Bore/stroke character | 1.085 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,688 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.898 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 46.4 ci |
| Static compression | 10:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 1.755" |
|---|---|
| Exhaust valve diameter | 1.563" |
| Chamber volume | 75 cc |
| Rocker ratio | 1.8:1 |
| Lifter type | hydraulic |
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These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1957 | 300 hp | — |
| 1957 | 312 hp | — |
| 1958 | 265 hp | — |