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Mercury 302 specs: 302 ci (5.0L) 8-cylinder, 4.00 x 3.00 in (101.6 x 76.2 mm) bore and stroke, 10:1 compression. Rated 230 hp. Rod ratio and piston speed.
The Mercury Windsor (302) is oversquare — the 4" bore exceeds the 3" stroke by 33.3% — a layout that favors airflow and RPM over leverage at the crank. The 3" stroke does not reach 4,000 ft/min of mean piston speed until about 8,000 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 37.8 ci (619 cc).
10:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
It is one of 24 engines in the Windsor family, sitting between the 221 ci and 351 ci members. Factory fitments include the Mercury Cougar, Mercury Montego, Mercury Cougar Eliminator.
| Displacement | 302 ci / 5 L |
|---|---|
| Bore | 4" |
| Stroke | 3" |
| Cylinders | 8 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 1.333 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 230 hp |
| Bore/stroke character | 1.333 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,000 ft/min — conservative for a street engine |
| Displacement per cylinder | 37.8 ci |
| Static compression | 10:1 — in the range that usually runs on pump premium |
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