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Subaru EJ specs: 2.457L (150 ci) 4-cylinder, 99.5 x 79 mm (3.9173 x 3.1102 in) bore and stroke, 10:1 compression. Rated 165-175 hp. SOHC.
The Subaru EJ is oversquare — the 3.9173" bore exceeds the 3.1102" stroke by 26.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.1102" stroke does not reach 4,000 ft/min of mean piston speed until about 7,700 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 37.5 ci (615 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 37 engines in the EJ family, sitting between the 91.1 ci and 152 ci members. 3 factory variants share these dimensions, rated from 165 to 175 hp. Factory fitments include the Subaru Legacy, Subaru Outback, Subaru Forester and 4 others.
| Displacement | 150 ci / 2.457 L |
|---|---|
| Bore | 3.9173" |
| Stroke | 3.1102" |
| Cylinders | 4 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 1.26 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | SOHC |
| Fuel type | gas |
| Advertised HP | 165–175 hp |
| Bore/stroke character | 1.260 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,110 ft/min — conservative for a street engine |
| Displacement per cylinder | 37.5 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 |
|---|---|---|
| — | 165 hp | EJ25 (NA SOHC), EJ251, EJ251/EJ253, EJ251/253 (NA SOHC), EJ25D, EJ25D (NA DOHC), EJ25 (NA DOHC) |
| — | 170 hp | EJ253 |
| — | 175 hp | EJ253 |