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Mazda BP-4W specs: 1.8L (112 ci) 4-cylinder, 83 x 85 mm (3.2677 x 3.3465 in) bore and stroke, 9.5:1 compression. Rated 140 hp. Rod ratio and piston speed.
The Mazda BP-4W is close to square: 3.2677" bore against 3.3465" stroke, within 2.4%, which splits the difference between a high-revving layout and a torque layout. The 3.3465" stroke does not reach 4,000 ft/min of mean piston speed until about 7,150 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 28.0 ci (459 cc).
9.5:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
It is one of 14 engines in the B-Series family, sitting between the 97 ci and 112.2 ci members. Factory fitments include the MX-5 Miata NB.
| Displacement | 112 ci / 1.8 L |
|---|---|
| Bore | 3.2677" |
| Stroke | 3.3465" |
| Cylinders | 4 |
| Compression ratio | 9.5:1 |
| Bore/stroke ratio | 0.976 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 140 hp |
| Bore/stroke character | 0.976 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,347 ft/min — conservative for a street engine |
| Displacement per cylinder | 28.0 ci |
| Static compression | 9.5:1 — in the range that usually runs on pump premium |
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