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Honda K20C9 specs: 2.0L (121.9 ci) 4-cylinder, 86 x 86 mm (3.3858 x 3.3858 in) bore and stroke. Rated 150 hp, 2025–2026. Used in the Honda Civic. DOHC.
The Honda K20C9 is exactly square — 3.3858" bore and 3.3858" stroke are the same — which splits the difference between a high-revving layout and a torque layout. 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 4 cylinders displaces 30.5 ci (499 cc).
It is one of 15 engines in the K-series family, the smallest at 121.9 ci. 2 factory variants share these dimensions, rated at 150 hp across 2025–2026.
| Displacement | 121.9 ci / 2 L |
|---|---|
| Bore | 3.3858" |
| Stroke | 3.3858" |
| Cylinders | 4 |
| Configuration | I4 |
| Bore/stroke ratio | 1 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 150 hp |
| Years | 2025–2026 |
| Bore/stroke character | 1.000 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,386 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.5 ci |
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 | 150 hp | K20C9 |
| 2026 | 150 hp | K20C9 |