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Mercury J-code specs: 302 ci (5.0L) 8-cylinder, 4.00 x 3.00 in (101.6 x 76.2 mm) bore and stroke. Rated 230 hp, 1968. Used in the Mercury Cougar. OHV.
The Mercury J-code 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).
It is one of 24 engines in the Windsor family, sitting between the 221 ci and 351 ci members.
| Displacement | 302 ci / 5 L |
|---|---|
| Bore | 4" |
| Stroke | 3" |
| Cylinders | 8 |
| Configuration | V8 |
| Bore/stroke ratio | 1.333 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 230 hp |
| Years | 1968 |
| 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 |
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