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Porsche 528 specs: 1.5L (91 ci) 4-cylinder, 80 x 74 mm (3.1496 x 2.9134 in) bore and stroke, 8.2:1 compression. Rated 70 hp, 1953–1955.
The Porsche 91ci (528) is oversquare — the 3.1496" bore exceeds the 2.9134" stroke by 8.1% — a layout that favors airflow and RPM over leverage at the crank. The 2.9134" stroke does not reach 4,000 ft/min of mean piston speed until about 8,250 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).
8.2:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Porsche 91ci family, all of them 91 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated at 70 hp across 1953–1955.
| Displacement | 91 ci / 1.5 L |
|---|---|
| Bore | 3.1496" |
| Stroke | 2.9134" |
| Cylinders | 4 |
| Compression ratio | 8.2:1 * |
| Bore/stroke ratio | 1.081 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 70 hp |
| Years | 1953–1955 |
| Bore/stroke character | 1.081 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,913 ft/min — conservative for a street engine |
| Displacement per cylinder | 22.8 ci |
| Static compression | 8.2:1 — 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 |
|---|---|---|
| 1953 | 70 hp | 528 |
| 1954 | 70 hp | 528 |
| 1955 | 70 hp | 528 |
1 factory vehicle, 1953–1955. Each year opens that model's engine table.