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Mazda 12A Turbo specs: 1.146L (70 ci) 2-cylinder, 105 x 70 mm (4.1339 x 2.7559 in) bore and stroke, 8.5:1 compression. Rated 160 hp. Rotary.
The Mazda 12A Turbo is oversquare — the 4.1339" bore exceeds the 2.7559" stroke by 50.0% — 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 35.0 ci (574 cc).
8.5:1 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, sitting between the 59.9 ci and 119.7 ci members. Factory fitments include the Mazda RX-7 (FB).
| Displacement | 70 ci / 1.146 L |
|---|---|
| Bore | 4.1339" |
| Stroke | 2.7559" |
| Cylinders | 2 |
| Compression ratio | 8.5:1 |
| Bore/stroke ratio | 1.5 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | Rotary |
| Fuel type | gas |
| Advertised HP | 160 hp |
| Bore/stroke character | 1.500 — 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 | 35.0 ci |
| Static compression | 8.5:1 — low by modern standards, generally happy on regular pump fuel |
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