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Mazda 10A specs: 0.982L (59.9 ci) 2-cylinder, 90 x 70 mm (3.5433 x 2.7559 in) bore and stroke, 9.4:1 compression. Rated 100 hp. Rod ratio and piston speed.
The Mazda Rotary (10A) is oversquare — the 3.5433" bore exceeds the 2.7559" stroke by 28.6% — a layout that favors airflow and RPM over leverage at the crank. The 2.7559" stroke does not reach 4,000 ft/min of mean piston speed until about 8,700 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 2 cylinders displaces 30.0 ci (491 cc).
9.4:1 on aluminum heads is low by modern standards and generally happy on regular pump fuel.
It is one of 14 engines in the Rotary family, the smallest at 59.9 ci. Factory fitments include the Mazda Cosmo Sport, Mazda R100.
| Displacement | 59.9 ci / 0.982 L |
|---|---|
| Bore | 3.5433" |
| Stroke | 2.7559" |
| Cylinders | 2 |
| Compression ratio | 9.4:1 |
| Bore/stroke ratio | 1.286 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | Rotary |
| Fuel type | gas |
| Advertised HP | 100 hp |
| Bore/stroke character | 1.286 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,756 ft/min — conservative for a street engine |
| Displacement per cylinder | 29.9 ci |
| Static compression | 9.4:1 — low by modern standards, generally happy on regular pump fuel |
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