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Volkswagen Air-cooled Flat Four (1963–1966) specs: 1.5L (91.1 ci) 4-cylinder, 83 x 69 mm (3.2677 x 2.7165 in) bore and stroke. Rated 51-53 hp, 1963–1966.
The Volkswagen Air-cooled Flat Four (1963–1966) is oversquare — the 3.2677" bore exceeds the 2.7165" stroke by 20.3% — a layout that favors airflow and RPM over leverage at the crank. The 2.7165" stroke does not reach 4,000 ft/min of mean piston speed until about 8,850 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 22.8 ci (373 cc).
It is one of 28 engines in the Air-cooled Flat Four family, sitting between the 69 ci and 96.6 ci members. 4 factory variants share these dimensions, rated from 51 to 53 hp across 1963–1966.
| Displacement | 91.1 ci / 1.5 L |
|---|---|
| Bore | 3.2677" |
| Stroke | 2.7165" |
| Cylinders | 4 |
| Bore/stroke ratio | 1.203 |
| Block material | magnesium alloy |
|---|---|
| Head material | aluminum |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 51–53 hp |
| Years | 1963–1966 |
| Bore/stroke character | 1.203 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,717 ft/min — conservative for a street engine |
| Displacement per cylinder | 22.8 ci |
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 |
|---|---|---|
| 1963 | 51 hp | — |
| 1964 | 51 hp | — |
| 1965 | 51 hp | — |
| 1966 | 53 hp | — |
1 factory vehicle, 1963–1966. Each year opens that model's engine table.