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Ford 312ci specs: 312 ci (5.1L) 8-cylinder, 3.80 x 3.44 in (96.5 x 87.4 mm) bore and stroke, 9.7:1 compression. Rated 245-270 hp, 1957.
The Ford 312ci is oversquare — the 3.8" bore exceeds the 3.44" stroke by 10.5% — a layout that favors airflow and RPM over leverage at the crank. The 3.44" 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 39.0 ci (639 cc).
9.7:1 is in the range that usually runs on pump premium.
It is one of 5 engines in the Ford 312ci family, all of them 312 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated from 245 to 270 hp in 1957.
| Displacement | 312 ci / 5.1 L |
|---|---|
| Bore | 3.8" |
| Stroke | 3.44" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9.7:1 |
| Bore/stroke ratio | 1.105 |
| Block material | cast iron |
|---|---|
| Valvetrain | OHV |
| Induction | 4-bbl Holley |
| Fuel type | gas |
| Advertised HP | 245–270 hp |
| Years | 1957 |
| Bore/stroke character | 1.105 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,440 ft/min — conservative for a street engine |
| Displacement per cylinder | 39.0 ci |
| Static compression | 9.7:1 — 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 | 245 hp | — |
| 1957 | 270 hp | — |