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Subaru EJ255 specs: 2.5L (152 ci) 4-cylinder, 99.5 x 79 mm (3.9173 x 3.1102 in) bore and stroke, 8.4:1 compression. Rated 250 hp. Rod ratio and piston speed.
The Subaru EJ255 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).
8.4:1 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. Factory fitments include the Subaru Impreza WRX, Subaru Legacy GT, Subaru Forester XT.
| Displacement | 152 ci / 2.5 L |
|---|---|
| Bore | 3.9173" |
| Stroke | 3.1102" |
| Cylinders | 4 |
| Compression ratio | 8.4:1 |
| Bore/stroke ratio | 1.26 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 250 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 | 8.4:1 — low by modern standards, generally happy on regular pump fuel |
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