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Porsche MDG specs: 4.0L (244.1 ci) 6-cylinder, 102 x 81.5 mm (4.0157 x 3.2087 in) bore and stroke, 12.5:1 compression. Rated 394 hp, 2021–2025.
The Porsche 9A1 (MDG) is oversquare — the 4.0157" bore exceeds the 3.2087" stroke by 25.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.2087" stroke does not reach 4,000 ft/min of mean piston speed until about 7,500 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 40.7 ci (667 cc).
12.5:1 on aluminum heads is high for a production gasoline engine; running a ratio like that on pump fuel depends on chamber design and fuel delivery rather than the number alone.
It is one of 6 engines in the 9A1 family, the largest at 244.1 ci. 5 factory variants share these dimensions, rated at 394 hp across 2021–2025.
| Displacement | 244.1 ci / 4 L |
|---|---|
| Bore | 4.0157" |
| Stroke | 3.2087" |
| Cylinders | 6 |
| Compression ratio | 12.5:1 * |
| Bore/stroke ratio | 1.252 |
* Compression ratio from a single source; not yet cross-verified.
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 394 hp |
| Years | 2021–2025 |
| Bore/stroke character | 1.252 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,209 ft/min — conservative for a street engine |
| Displacement per cylinder | 40.7 ci |
| Static compression | 12.5:1 — high enough that pump premium or better is normally required |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 2021 | 394 hp | MDG |
| 2022 | 394 hp | MDG |
| 2023 | 394 hp | MDG |
| 2024 | 394 hp | MDG |
| 2025 | 394 hp | MDG |
1 factory vehicle, 2021–2025. Each year opens that model's engine table.