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Mercedes-Benz OM617.951 specs: 3.0L (183 ci) 5-cylinder, 90.9 x 92.4 mm (3.5787 x 3.6378 in) bore and stroke, 21.5:1 compression. Built 1981–1985.
The Mercedes-Benz OM617.951 is close to square: 3.5787" bore against 3.6378" stroke, within 1.6%, which splits the difference between a high-revving layout and a torque layout. The 3.6378" stroke puts mean piston speed at 4,000 ft/min around 6,600 RPM, which is where a production bottom end is generally considered at its limit. Each of the 5 cylinders displaces 36.6 ci (600 cc).
At 21.5:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
It is one of 17 engines in the Mercedes-Benz 183ci family, all of them 183 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions across 1981–1985.
| Displacement | 183 ci / 3 L |
|---|---|
| Bore | 3.5787" |
| Stroke | 3.6378" |
| Cylinders | 5 |
| Compression ratio | 21.5:1 |
| Bore/stroke ratio | 0.984 |
| Fuel type | diesel |
|---|---|
| Years | 1981–1985 |
| Bore/stroke character | 0.984 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,638 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 36.6 ci |
| Static compression | 21.5:1 — high enough that pump premium or better is normally required |
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 |
|---|---|---|
| 1981 | — | OM617.951 |
| 1984 | — | OM617.951 |
| 1985 | — | OM617.951 |
1 factory vehicle, 1981–1985. Each year opens that model's engine table.