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Mercedes-Benz M103 specs: 3.0L (181 ci) 6-cylinder, 88.5 x 80.2 mm (3.4843 x 3.1594 in) bore and stroke, 9.2:1 compression. Built 1986–1993.
The Mercedes-Benz M103 is oversquare — the 3.4843" bore exceeds the 3.1594" stroke by 10.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.1594" 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 6 cylinders displaces 30.2 ci (494 cc).
9.2:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Mercedes-Benz 181ci family, all of them 181 ci — the differences between them are in compression, heads and rating, not displacement. 8 factory variants share these dimensions across 1986–1993.
| Displacement | 181 ci / 3 L |
|---|---|
| Bore | 3.4843" |
| Stroke | 3.1594" |
| Cylinders | 6 |
| Configuration | I6 |
| Compression ratio | 9.2:1 |
| Bore/stroke ratio | 1.103 |
| Fuel type | gas |
|---|---|
| Years | 1986–1993 |
| Bore/stroke character | 1.103 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,159 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.2 ci |
| Static compression | 9.2:1 — 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 |
|---|---|---|
| 1986 | — | M103 |
| 1987 | — | M103 |
| 1988 | — | M103 |
| 1989 | — | M103 |
| 1990 | — | M103 |
| 1991 | — | M103 |
| 1992 | — | M103 |
| 1993 | — | M103 |
2 factory vehicles, 1986–1993. Each year opens that model's engine table.