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Mercedes-Benz M278 specs: 4.7L (285 ci) 8-cylinder, 92.9 x 86 mm (3.6575 x 3.3858 in) bore and stroke, 10.5:1 compression. Rated 402 hp, 2012–2020.
The Mercedes-Benz M278 is oversquare — the 3.6575" bore exceeds the 3.3858" stroke by 8.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.3858" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 35.6 ci (584 cc).
10.5:1 is in the range that usually runs on pump premium.
15 factory variants share these dimensions, rated at 402 hp across 2012–2020.
| Displacement | 285 ci / 4.7 L |
|---|---|
| Bore | 3.6575" |
| Stroke | 3.3858" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 10.5:1 * |
| Bore/stroke ratio | 1.08 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 402 hp |
| Years | 2012–2020 |
| Bore/stroke character | 1.080 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,386 ft/min — conservative for a street engine |
| Displacement per cylinder | 35.6 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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 |
|---|---|---|
| 2012 | — | M278 |
| 2012 | 402 hp | M278 |
| 2013 | — | M278 |
| 2013 | 402 hp | M278 |
| 2014 | — | M278 |
| 2014 | 402 hp | M278 |
| 2015 | — | M278 |
| 2015 | 402 hp | M278 |
| 2016 | — | M278 |
| 2016 | 402 hp | M278 |
| 2017 | — | M278 |
| 2017 | 402 hp | M278 |
| 2018 | — | M278 |
| 2019 | — | M278 |
| 2020 | — | M278 |
3 factory vehicles, 2012–2020. Each year opens that model's engine table.