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Porsche Mezger 3.8 specs: 231.71 ci 6-cylinder, 102.7 x 76.4 mm (4.0433 x 3.0079 in) bore and stroke. Rod ratio and piston speed worked out.
The Porsche Mezger 3.8 is oversquare — the 4.0433" bore exceeds the 3.0079" stroke by 34.4% — 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 38.6 ci (633 cc).
It is one of 7 engines in the Mezger family, sitting between the 219.7 ci and 243.9 ci members.
| Displacement | 231.71 ci |
|---|---|
| Bore | 4.0433" |
| Stroke | 3.0079" |
| Cylinders | 6 |
| Compression ratio | 12–12.2:1 (published figures vary) |
| Bore/stroke ratio | 1.344 |
| Fuel type | gas |
|---|
| Bore/stroke character | 1.344 — 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 | 38.6 ci |
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