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Porsche Mezger 4.0 specs: 243.9 ci 6-cylinder, 102.7 x 80.4 mm (4.0433 x 3.1654 in) bore and stroke, 12.6:1 compression. Rod ratio and piston speed.
The Porsche Mezger 4.0 is oversquare — the 4.0433" bore exceeds the 3.1654" stroke by 27.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.1654" stroke does not reach 4,000 ft/min of mean piston speed until about 7,600 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 (666 cc).
12.6:1 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 7 engines in the Mezger family, the largest at 243.9 ci.
| Displacement | 243.9 ci |
|---|---|
| Bore | 4.0433" |
| Stroke | 3.1654" |
| Cylinders | 6 |
| Compression ratio | 12.6:1 |
| Bore/stroke ratio | 1.277 |
| Fuel type | gas |
|---|
| Bore/stroke character | 1.277 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,165 ft/min — conservative for a street engine |
| Displacement per cylinder | 40.6 ci |
| Static compression | 12.6:1 — high enough that pump premium or better is normally required |
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