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BMW M20B27 specs: 2.7L (164 ci) 6-cylinder, 84 x 81 mm (3.3071 x 3.1890 in) bore and stroke. Rated 121-127 hp, 1982–1988. Used in the BMW 5 Series.
The BMW M20B27 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 6 cylinders displaces 27.3 ci (448 cc).
8 factory variants share these dimensions, rated from 121 to 127 hp across 1982–1988.
| Displacement | 164 ci / 2.7 L |
|---|---|
| Bore | 3.3071" |
| Stroke | 3.189" |
| Cylinders | 6 |
| Configuration | I6 |
| Compression ratio | 8.5–9:1 (published figures vary) |
| Bore/stroke ratio | 1.037 |
| Fuel type | gas |
|---|---|
| Advertised HP | 121–127 hp |
| Years | 1982–1988 |
| 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 | 27.3 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 |
|---|---|---|
| 1982 | 121 hp | M20B27 |
| 1983 | 121 hp | M20B27 |
| 1984 | 121 hp | M20B27 |
| 1985 | 121 hp | M20B27 |
| 1986 | 121 hp | M20B27 |
| 1987 | 121 hp | M20B27 |
| 1988 | — | M20B27 |
| 1988 | 127 hp | M20B27 |
2 factory vehicles, 1982–1988. Each year opens that model's engine table.