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Porsche 30 9A2 991 Turbo specs: 3.0L (181.9 ci) 6-cylinder, 91 x 76.4 mm (3.5827 x 3.0079 in) bore and stroke, 10:1 compression. Rated 370 hp. DOHC.
The Porsche 30 9A2 991 Turbo is oversquare — the 3.5827" bore exceeds the 3.0079" stroke by 19.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.0079" stroke does not reach 4,000 ft/min of mean piston speed until about 8,000 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 30.3 ci (497 cc).
10:1 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 3 engines in the 9A2 family, all of them 181.9 ci — the differences between them are in compression, heads and rating, not displacement. Factory fitments include the 911 Carrera (991.2).
| Displacement | 181.9 ci / 3 L |
|---|---|
| Bore | 3.5827" |
| Stroke | 3.0079" |
| Cylinders | 6 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 1.191 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 370 hp |
| Bore/stroke character | 1.191 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,008 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.3 ci |
| Static compression | 10:1 — in the range that usually runs on pump premium |
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