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Mercury Duratec specs: 155 ci (2.5L) 6-cylinder, 3.244 x 3.13 in (82.4 x 79.5 mm) bore and stroke, 9.7:1 compression. Rated 170 hp, 1999–2002.
The Mercury Duratec is close to square: 3.2441" bore against 3.1299" stroke, within 3.6%, which splits the difference between a high-revving layout and a torque layout. The 3.1299" stroke does not reach 4,000 ft/min of mean piston speed until about 7,650 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 25.8 ci (423 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. 4 factory variants share these dimensions, rated at 170 hp across 1999–2002.
| Displacement | 155 ci / 2.5 L |
|---|---|
| Bore | 3.2441" |
| Stroke | 3.1299" |
| Cylinders | 6 |
| Compression ratio | 9.7:1 |
| Bore/stroke ratio | 1.036 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Induction | sequential multi-port EFI |
| Fuel type | gas |
| Advertised HP | 170 hp |
| Years | 1999–2002 |
| Bore/stroke character | 1.036 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,130 ft/min — conservative for a street engine |
| Displacement per cylinder | 25.8 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 |
|---|---|---|
| 1999 | 170 hp | — |
| 2000 | 170 hp | — |
| 2001 | 170 hp | — |
| 2002 | 170 hp | — |