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Mercury 255ci (1952–1953) specs: 255 ci 8-cylinder, 3.188 x 4.00 in (81 x 101.6 mm) bore and stroke, 7.2:1 compression. Rated 125 hp, 1952–1953.
The Mercury 255ci (1952–1953) is undersquare — the 4" stroke exceeds the 3.1875" bore by 20.3% — a layout that trades peak RPM for leverage and torque low in the range. The 4" stroke puts mean piston speed at 4,000 ft/min around 6,000 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 31.9 ci (522 cc).
7.2:1 is low by modern standards and generally happy on regular pump fuel.
2 factory variants share these dimensions, rated at 125 hp across 1952–1953.
| Displacement | 255 ci |
|---|---|
| Bore | 3.1875" |
| Stroke | 4" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 7.2:1 * |
| Bore/stroke ratio | 0.797 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 125 hp |
| Years | 1952–1953 |
| Bore/stroke character | 0.797 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,000 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 31.9 ci |
| Static compression | 7.2:1 — 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 |
|---|---|---|
| 1952 | 125 hp | — |
| 1953 | 125 hp | — |
1 factory vehicle, 1952–1953. Each year opens that model's engine table.