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Volkswagen CB specs: 1.7L (102.5 ci) 4-cylinder, 90 x 66 mm (3.5433 x 2.5984 in) bore and stroke. Rod ratio and piston speed worked out.
The Volkswagen Type 4 Air-cooled (CB) is oversquare — the 3.5433" bore exceeds the 2.5984" stroke by 36.4% — a layout that favors airflow and RPM over leverage at the crank. The 2.5984" stroke does not reach 4,000 ft/min of mean piston speed until about 9,250 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 25.6 ci (420 cc).
It is one of 5 engines in the Type 4 Air-cooled family, the smallest at 102.5 ci.
| Displacement | 102.5 ci / 1.7 L |
|---|---|
| Bore | 3.5433" |
| Stroke | 2.5984" |
| Cylinders | 4 |
| Bore/stroke ratio | 1.364 |
| Fuel type | gas |
|---|
| Bore/stroke character | 1.364 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,598 ft/min — conservative for a street engine |
| Displacement per cylinder | 25.6 ci |
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