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BMW M10B18 specs: 1.8L (108 ci) 4-cylinder, 89 x 71 mm (3.5039 x 2.7953 in) bore and stroke, 8.8:1 compression. Rated 101 hp, 1980–1985.
The BMW M10B18 is oversquare — the 3.5039" bore exceeds the 2.7953" stroke by 25.3% — a layout that favors airflow and RPM over leverage at the crank. The 2.7953" stroke does not reach 4,000 ft/min of mean piston speed until about 8,600 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 27.0 ci (442 cc).
8.8:1 is low by modern standards and generally happy on regular pump fuel.
6 factory variants share these dimensions, rated at 101 hp across 1980–1985.
| Displacement | 108 ci / 1.8 L |
|---|---|
| Bore | 3.5039" |
| Stroke | 2.7953" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 8.8:1 * |
| Bore/stroke ratio | 1.253 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 101 hp |
| Years | 1980–1985 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1983 | M10B18 net | 101 | — | — |
| 1984 | M10B18 net | 101 | — | — |
| 1985 | M10B18 net | 101 | — | — |
Factory specification sheet.
| Bore/stroke character | 1.253 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,795 ft/min — conservative for a street engine |
| Displacement per cylinder | 27.0 ci |
| Static compression | 8.8:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| 1980 | 101 hp | M10B18 |
| 1981 | 101 hp | M10B18 |
| 1982 | 101 hp | M10B18 |
| 1983 | 101 hp | M10B18 |
| 1984 | 101 hp | M10B18 |
| 1985 | 101 hp | M10B18 |
1 factory vehicle, 1980–1985. Each year opens that model's engine table.