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Oldsmobile 371ci (1957–1958) 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 305-312 hp.
The Oldsmobile 371ci (1957–1958) 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 5 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 305 to 312 hp across 1957–1958.
| Displacement | 371 ci / 6.1 L |
|---|---|
| Bore | 4" |
| Stroke | 3.688" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 10:1 |
| Rod length | 7" |
| Rod ratio | 1.898 |
| Bore/stroke ratio | 1.085 |
| Fuel type | gas |
|---|---|
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 305–312 hp |
| Years | 1957–1958 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1958 | gross | 305 @ 4600 | 410 lb-ft @ 2800 | 10:1 |
| 1958 | J-2 gross | 312 @ 4600 | 415 lb-ft @ 2800 | 10:1 |
Factory specification sheet.
| 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 |
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 |
|---|---|---|
| 1957 | — | — |
| 1958 | 305 hp | — |
| 1958 | 312 hp | — |
2 factory vehicles, 1957–1958. Each year opens that model's engine table.