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BMW M42B18 specs: 1.8L (110 ci) 4-cylinder, 84 x 81 mm (3.3071 x 3.1890 in) bore and stroke, 10:1 compression. Rated 134-138 hp, 1991–1995.
The BMW M42B18 is close to square: 3.3071" bore against 3.189" stroke, within 3.7%, which splits the difference between a high-revving layout and a torque layout. The 3.189" stroke does not reach 4,000 ft/min of mean piston speed until about 7,550 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 27.5 ci (451 cc).
10:1 is in the range that usually runs on pump premium.
6 factory variants share these dimensions, rated from 134 to 138 hp across 1991–1995.
| Displacement | 110 ci / 1.8 L |
|---|---|
| Bore | 3.3071" |
| Stroke | 3.189" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 10:1 * |
| Bore/stroke ratio | 1.037 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 134–138 hp |
| Years | 1991–1995 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1991 | M42B18 net | 134 | — | — |
| 1992 | M42B18 net | 134 | — | — |
Factory specification sheet.
| Bore/stroke character | 1.037 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,189 ft/min — conservative for a street engine |
| Displacement per cylinder | 27.5 ci |
| Static compression | 10:1 — in the range that usually runs on pump premium |
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 |
|---|---|---|
| 1991 | 134 hp | M42B18 |
| 1992 | 134 hp | M42B18 |
| 1992 | 138 hp | M42B18 |
| 1993 | 138 hp | M42B18 |
| 1994 | 138 hp | M42B18 |
| 1995 | 138 hp | M42B18 |
1 factory vehicle, 1991–1995. Each year opens that model's engine table.