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Mercedes-Benz M177 + rear e-motor specs: 4.0L (243 ci) 8-cylinder, 83 x 92 mm (3.2677 x 3.6220 in) bore and stroke, 8.6:1 compression. Built 2025–2026.
The Mercedes-Benz M177 + 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 8 cylinders displaces 30.4 ci (498 cc).
8.6:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Mercedes-Benz 243ci family, all of them 243 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions across 2025–2026.
| Displacement | 243 ci / 4 L |
|---|---|
| Bore | 3.2677" |
| Stroke | 3.622" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.6:1 |
| Bore/stroke ratio | 0.902 |
| Fuel type | gas |
|---|---|
| Years | 2025–2026 |
| 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 | 30.4 ci |
| Static compression | 8.6:1 — 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 |
|---|---|---|
| 2025 | — | M177 + rear e-motor |
| 2026 | — | M177 + rear e-motor |
2 factory vehicles, 2025–2026. Each year opens that model's engine table.