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Subaru EJ specs: 2.5L (152 ci) 4-cylinder, 99.5 x 79 mm (3.9173 x 3.1102 in) bore and stroke, 8.2:1 compression. Rated 210-300 hp. Rod ratio and piston speed.
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 38.0 ci (623 cc).
8.2:1 on aluminum heads is low by modern standards and generally happy on regular pump fuel.
It is one of 37 engines in the EJ family, the largest at 152 ci. 6 factory variants share these dimensions, rated from 210 to 300 hp. Factory fitments include the Subaru Impreza WRX STI, Subaru Legacy GT, Subaru Forester XT and 8 others.
| Displacement | 152 ci / 2.5 L |
|---|---|
| Bore | 3.9173" |
| Stroke | 3.1102" |
| Cylinders | 4 |
| Compression ratio | 8.2:1 |
| Bore/stroke ratio | 1.26 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 210–300 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 | 38.0 ci |
| Static compression | 8.2:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| — | 210 hp | EJ255 (Turbo SOHC), EJ255 |
| — | 250 hp | EJ255 |
| — | 265 hp | EJ255 (Turbo WRX), EJ255 |
| — | 300 hp | EJ257 |
| — | 300 hp | EJ257 (Turbo STI) |
| — | 300 hp | EJ257 |