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Volkswagen AJ specs: 1.6L (96.6 ci) 4-cylinder, 85.5 x 69 mm (3.3661 x 2.7165 in) bore and stroke, 7.3:1 compression. Rated 48 hp, 1975–1979.
The Volkswagen Air-cooled Flat Four (AJ) is oversquare — the 3.3661" bore exceeds the 2.7165" stroke by 23.9% — 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 24.2 ci (396 cc).
7.3:1 on aluminum heads is low by modern standards and generally happy on regular pump fuel.
It is one of 13 engines in the Air-cooled Flat Four family, the largest at 96.6 ci. 5 factory variants share these dimensions, rated at 48 hp across 1975–1979.
| Displacement | 96.6 ci / 1.6 L |
|---|---|
| Bore | 3.3661" |
| Stroke | 2.7165" |
| Cylinders | 4 |
| Compression ratio | 7.3:1 |
| Bore/stroke ratio | 1.239 |
| Block material | magnesium alloy |
|---|---|
| Head material | aluminum |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 48 hp |
| Years | 1975–1979 |
| Bore/stroke character | 1.239 — 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 | 24.1 ci |
| Static compression | 7.3:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| 1975 | 48 hp | AJ |
| 1976 | 48 hp | AJ |
| 1977 | 48 hp | AJ |
| 1978 | 48 hp | AJ |
| 1979 | 48 hp | AJ |