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Mercedes-Benz OM651 specs: 2.1L (131 ci) 4-cylinder, 83 x 99 mm (3.2677 x 3.8976 in) bore and stroke, 16.2:1 compression. Rated 161-195 hp, 2014–2022.
The Mercedes-Benz OM651 is undersquare — the 3.8976" stroke exceeds the 3.2677" bore by 16.2% — a layout that trades peak RPM for leverage and torque low in the range. The 3.8976" stroke puts mean piston speed at 4,000 ft/min around 6,150 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 32.8 ci (537 cc).
At 16.2:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
10 factory variants share these dimensions, rated from 161 to 195 hp across 2014–2022.
| Displacement | 131 ci / 2.1 L |
|---|---|
| Bore | 3.2677" |
| Stroke | 3.8976" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 16.2:1 * |
| Bore/stroke ratio | 0.838 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | diesel |
|---|---|
| Advertised HP | 161–195 hp |
| Years | 2014–2022 |
| Bore/stroke character | 0.838 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,898 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 32.8 ci |
| Static compression | 16.2:1 — 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 |
|---|---|---|
| 2014 | 161 hp | OM651 |
| 2014 | 195 hp | OM651 |
| 2015 | 161 hp | OM651 |
| 2015 | 195 hp | OM651 |
| 2016 | 161 hp | OM651 |
| 2016 | 195 hp | OM651 |
| 2017 | 161 hp | OM651 |
| 2018 | 161 hp | OM651 |
| 2021 | — | OM651 |
| 2022 | — | OM651 |
2 factory vehicles, 2014–2022. Each year opens that model's engine table.