Mercury 255 Specs
Mercury 255 engine specs: 255 ci (4.2L), 8-cylinder, 3.6811" bore x 3" stroke, 8.2:1 compression.
Dimensions
| Displacement | 255 ci / 4.2 L |
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| Bore | 3.6811" |
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| Stroke | 3" |
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| Cylinders | 8 |
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| Compression ratio | 8.2:1 |
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| Bore/stroke ratio | 1.227 |
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Construction
| Block material | cast iron |
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| Head material | cast iron |
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| Valvetrain | OHV |
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| Fuel type | gas |
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| Advertised HP | 115–120 hp |
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What these numbers mean
| Bore/stroke character | 1.227 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
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| Mean piston speed at 6,000 RPM | 3,000 ft/min — conservative for a street engine |
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| Displacement per cylinder | 31.9 ci |
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| Static compression | 8.2:1 — low by modern standards, generally happy on regular pump fuel |
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Variants sharing these dimensions (2)
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
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| — | 115 hp | 255 |
| — | 120 hp | 255 |
Vehicles (2)
- Mercury Grand Marquis
- Mercury Cougar
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