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Subaru FB16 specs: 1.6L (97.6 ci) 4-cylinder, 78.8 x 82 mm (3.1024 x 3.2283 in) bore and stroke, 10.5:1 compression. Rated 114 hp. Rod ratio and piston speed.
The Subaru FB16 is close to square: 3.1024" bore against 3.2283" stroke, within 3.9%, which splits the difference between a high-revving layout and a torque layout. 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 4 cylinders displaces 24.4 ci (400 cc).
10.5:1 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.
It is one of 4 engines in the FB family, the smallest at 97.6 ci. Factory fitments include the Subaru Impreza, Subaru XV.
| Displacement | 97.6 ci / 1.6 L |
|---|---|
| Bore | 3.1024" |
| Stroke | 3.2283" |
| Cylinders | 4 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 0.961 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 114 hp |
| Bore/stroke character | 0.961 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,228 ft/min — conservative for a street engine |
| Displacement per cylinder | 24.4 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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