See other engines in this family
BMW M10 specs: 2.0L (121 ci) 4-cylinder, 89 x 80 mm (3.5039 x 3.1496 in) bore and stroke. Rated 100-130 hp, 1968–1976. Used in the BMW 2002.
The BMW 121ci (M10) is oversquare — the 3.5039" bore exceeds the 3.1496" stroke by 11.2% — 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 4 cylinders displaces 30.3 ci (496 cc).
It is one of 2 engines in the BMW 121ci family, all of them 121 ci — the differences between them are in compression, heads and rating, not displacement. 12 factory variants share these dimensions, rated from 100 to 130 hp across 1968–1976.
| Displacement | 121 ci / 2 L |
|---|---|
| Bore | 3.5039" |
| Stroke | 3.1496" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 8.5–9.5:1 (published figures vary) |
| Bore/stroke ratio | 1.112 |
| Fuel type | gas |
|---|---|
| Advertised HP | 100–130 hp |
| Years | 1968–1976 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1972 | M10 net | 130 | 130 lb-ft | — |
| 1973 | M10 net | 130 | 130 lb-ft | — |
| 1974 | M10 net | 130 | 130 lb-ft | — |
Factory specification sheet.
| Bore/stroke character | 1.112 — 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 | 30.3 ci |
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 |
|---|---|---|
| 1968 | 100 hp | M10 |
| 1969 | 100 hp | M10 |
| 1970 | 100 hp | M10 |
| 1971 | 100 hp | M10 |
| 1972 | 100 hp | M10 |
| 1972 | 130 hp | M10 |
| 1973 | 100 hp | M10 |
| 1973 | 130 hp | M10 |
| 1974 | 100 hp | M10 |
| 1974 | 130 hp | M10 |
| 1975 | 100 hp | M10 |
| 1976 | 100 hp | M10 |
1 factory vehicle, 1968–1976. Each year opens that model's engine table.