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Subaru ER27 specs: 2.672L (163.1 ci) 6-cylinder, 92 x 67 mm (3.6220 x 2.6378 in) bore and stroke, 9.5:1 compression. Rated 145 hp. Rod ratio and piston speed.
The Subaru ER27 is oversquare — the 3.622" bore exceeds the 2.6378" stroke by 37.3% — a layout that favors airflow and RPM over leverage at the crank. The 2.6378" stroke does not reach 4,000 ft/min of mean piston speed until about 9,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 27.2 ci (445 cc).
9.5:1 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.
Factory fitments include the Subaru XT6.
| Displacement | 163.1 ci / 2.672 L |
|---|---|
| Bore | 3.622" |
| Stroke | 2.6378" |
| Cylinders | 6 |
| Compression ratio | 9.5:1 |
| Bore/stroke ratio | 1.373 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | SOHC |
| Fuel type | gas |
| Advertised HP | 145 hp |
| Bore/stroke character | 1.373 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,638 ft/min — conservative for a street engine |
| Displacement per cylinder | 27.2 ci |
| Static compression | 9.5:1 — in the range that usually runs on pump premium |
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