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Mercury 4.0 SOHC specs: 245 ci (4.0L) 6-cylinder, 3.953 x 3.323 in (100.4 x 84.4 mm) bore and stroke, 9.7:1 compression. Rated 210 hp. SOHC.
The Mercury 4.0 SOHC is oversquare — the 3.9528" bore exceeds the 3.3228" stroke by 19.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.3228" stroke does not reach 4,000 ft/min of mean piston speed until about 7,200 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 40.8 ci (669 cc).
9.7:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
It is one of 10 engines in the Cologne family, sitting between the 170 ci and 256 ci members. Factory fitments include the Mercury Mountaineer.
| Displacement | 245 ci / 4 L |
|---|---|
| Bore | 3.9528" |
| Stroke | 3.3228" |
| Cylinders | 6 |
| Compression ratio | 9.7:1 |
| Bore/stroke ratio | 1.19 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | SOHC |
| Fuel type | gas |
| Advertised HP | 210 hp |
| Bore/stroke character | 1.190 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,323 ft/min — conservative for a street engine |
| Displacement per cylinder | 40.8 ci |
| Static compression | 9.7:1 — in the range that usually runs on pump premium |
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