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Mazda 20B-REW specs: 1.962L (119.7 ci) 3-cylinder, 105 x 80 mm (4.1339 x 3.1496 in) bore and stroke, 9:1 compression. Rated 280 hp. Rotary.
The Mazda 20B-REW is oversquare — the 4.1339" bore exceeds the 3.1496" stroke by 31.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.1496" stroke does not reach 4,000 ft/min of mean piston speed until about 7,600 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 3 cylinders displaces 39.9 ci (654 cc).
9:1 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 largest at 119.7 ci. Factory fitments include the Mazda Eunos Cosmo.
| Displacement | 119.7 ci / 1.962 L |
|---|---|
| Bore | 4.1339" |
| Stroke | 3.1496" |
| Cylinders | 3 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.313 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | Rotary |
| Fuel type | gas |
| Advertised HP | 280 hp |
| Bore/stroke character | 1.313 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,150 ft/min — conservative for a street engine |
| Displacement per cylinder | 39.9 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
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