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Mercedes-Benz M139l + rear e-motor specs: 2.0L (121 ci) 4-cylinder, 83 x 92 mm (3.2677 x 3.6220 in) bore and stroke, 9:1 compression. Built 2024–2025.
The Mercedes-Benz M139l + rear e-motor is undersquare — the 3.622" stroke exceeds the 3.2677" bore by 9.8% — a layout that trades peak RPM for leverage and torque low in the range. The 3.622" stroke puts mean piston speed at 4,000 ft/min around 6,650 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 30.3 ci (496 cc).
9:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 5 engines in the Mercedes-Benz 121ci family, all of them 121 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions across 2024–2025.
| Displacement | 121 ci / 2 L |
|---|---|
| Bore | 3.2677" |
| Stroke | 3.622" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 9:1 * |
| Bore/stroke ratio | 0.902 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Years | 2024–2025 |
| Bore/stroke character | 0.902 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,622 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 30.3 ci |
| Static compression | 9:1 — 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 |
|---|---|---|
| 2024 | — | M139l + rear e-motor |
| 2025 | — | M139l + rear e-motor |
1 factory vehicle, 2024–2025. Each year opens that model's engine table.