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Mercury 260 specs: 260 ci (4.2L) 8-cylinder, 3.799 x 2.87 in (96.5 x 72.9 mm) bore and stroke, 8.8:1 compression. Rated 164 hp. Rod ratio and piston speed.
The Mercury Windsor (260) is oversquare — the 3.7992" bore exceeds the 2.8701" stroke by 32.4% — a layout that favors airflow and RPM over leverage at the crank. The 2.8701" stroke does not reach 4,000 ft/min of mean piston speed until about 8,350 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 32.5 ci (533 cc).
8.8:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 24 engines in the Windsor family, sitting between the 221 ci and 351 ci members. Factory fitments include the Mercury Comet, Mercury Meteor.
| Displacement | 260 ci / 4.2 L |
|---|---|
| Bore | 3.7992" |
| Stroke | 2.8701" |
| Cylinders | 8 |
| Compression ratio | 8.8:1 |
| Bore/stroke ratio | 1.324 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 164 hp |
| Bore/stroke character | 1.324 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,870 ft/min — conservative for a street engine |
| Displacement per cylinder | 32.5 ci |
| Static compression | 8.8:1 — low by modern standards, generally happy on regular pump fuel |
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