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Subaru FA24F specs: 2.4L (146.5 ci) 4-cylinder, 94 x 86 mm (3.7008 x 3.3858 in) bore and stroke, 10.6:1 compression. Rated 271 hp. Rod ratio and piston speed.
The Subaru FA24F is oversquare — the 3.7008" bore exceeds the 3.3858" stroke by 9.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.3858" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 36.6 ci (600 cc).
10.6:1 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 11 engines in the FA family, the largest at 146.5 ci. Factory fitments include the Subaru WRX.
| Displacement | 146.5 ci / 2.4 L |
|---|---|
| Bore | 3.7008" |
| Stroke | 3.3858" |
| Cylinders | 4 |
| Compression ratio | 10.6:1 |
| Bore/stroke ratio | 1.093 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 271 hp |
| Bore/stroke character | 1.093 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,386 ft/min — conservative for a street engine |
| Displacement per cylinder | 36.6 ci |
| Static compression | 10.6:1 — in the range that usually runs on pump premium |
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