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Mercury 2.5L I4 specs: 152 ci (2.5L) 4-cylinder, 3.504 x 3.937 in (89 x 100 mm) bore and stroke, 9.7:1 compression. Rated 175 hp. Rod ratio and piston speed.
The Mercury 2.5L I4 is undersquare — the 3.937" stroke exceeds the 3.5039" bore by 11.0% — a layout that trades peak RPM for leverage and torque low in the range. The 3.937" stroke puts mean piston speed at 4,000 ft/min around 6,100 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 38.0 ci (623 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 12 engines in the Duratec family, sitting between the 140 ci and 227 ci members. 2 factory variants share these dimensions, rated at 175 hp. Factory fitments include the Mercury Milan, Mercury Mariner, Milan and 1 other.
| Displacement | 152 ci / 2.5 L |
|---|---|
| Bore | 3.5039" |
| Stroke | 3.937" |
| Cylinders | 4 |
| Compression ratio | 9.7:1 |
| Bore/stroke ratio | 0.89 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 175 hp |
| Bore/stroke character | 0.890 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,937 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 38.0 ci |
| Static compression | 9.7:1 — in the range that usually runs on pump premium |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| — | 175 hp | 2.5L I4 |
| — | 175 hp | 2.5L Duratec 25, Duratec 25, 2.5L Duratec, 2.5 I4, 2.5L, 2.5L I4 |