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Ford Fox specs: 61 ci (1.0L) 3-cylinder, 2.831 x 3.228 in (71.9 x 82 mm) bore and stroke, 10:1 compression. Rated 100-140 hp. Rod ratio and piston speed.
The Ford EcoBoost (Fox) is undersquare — the 3.2283" stroke exceeds the 2.8307" bore by 12.3% — a layout that trades peak RPM for leverage and torque low in the range. The 3.2283" stroke does not reach 4,000 ft/min of mean piston speed until about 7,450 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 3 cylinders displaces 20.3 ci (333 cc).
10:1 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 24 engines in the EcoBoost family, the smallest at 61 ci. 3 factory variants share these dimensions, rated from 100 to 140 hp. Factory fitments include the Ford Fiesta, Ford Focus, Ford B-Max and 6 others.
| Displacement | 61 ci / 1 L |
|---|---|
| Bore | 2.8307" |
| Stroke | 3.2283" |
| Cylinders | 3 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 0.877 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 100–140 hp |
| Bore/stroke character | 0.877 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,228 ft/min — conservative for a street engine |
| Displacement per cylinder | 20.3 ci |
| Static compression | 10:1 — 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 |
|---|---|---|
| — | 100 hp | Fox |
| — | 125 hp | Fox |
| — | 140 hp | Fox |