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Honda R18Z1 specs: 1.8L (109.8 ci) 4-cylinder, 81 x 87.3 mm (3.1890 x 3.4370 in) bore and stroke. Rated 110-143 hp, 2012–2015. Used in the Honda Civic. SOHC.
The Honda R18Z1 is undersquare — the 3.437" stroke exceeds the 3.189" bore by 7.2% — a layout that trades peak RPM for leverage and torque low in the range. The 3.437" stroke puts mean piston speed at 4,000 ft/min around 7,000 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 27.5 ci (450 cc).
It is one of 4 engines in the R-series family, all of them 109.8 ci — the differences between them are in compression, heads and rating, not displacement. 8 factory variants share these dimensions, rated from 110 to 143 hp across 2012–2015.
| Displacement | 109.8 ci / 1.8 L |
|---|---|
| Bore | 3.189" |
| Stroke | 3.437" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 10.6–12.7:1 (published figures vary) |
| Bore/stroke ratio | 0.928 |
| Valvetrain | SOHC |
|---|---|
| Fuel type | gas |
| Advertised HP | 110–143 hp |
| Years | 2012–2015 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 2012 | R18Z1 net | 110 @ 6500 | 106 lb-ft @ 4300 | 12.7:1 |
| 2012 | R18Z1 net | 140 @ 6500 | 128 lb-ft @ 4300 | 10.6:1 |
| 2013 | R18Z1 net | 110 @ 6500 | 106 lb-ft @ 4300 | 12.7:1 |
| 2013 | R18Z1 net | 140 @ 6500 | 128 lb-ft @ 4300 | 10.6:1 |
| 2014 | R18Z1 net | 110 @ 6500 | 106 lb-ft @ 4300 | 12.7:1 |
| 2014 | R18Z1 net | 143 @ 6500 | 129 lb-ft @ 4300 | 10.6:1 |
| 2015 | R18Z1 net | 110 @ 6500 | 106 lb-ft @ 4300 | 12.7:1 |
| 2015 | R18Z1 net | 143 @ 6500 | 129 lb-ft @ 4300 | 10.6:1 |
Factory specification sheet.
| Bore/stroke character | 0.928 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,437 ft/min — conservative for a street engine |
| Displacement per cylinder | 27.4 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 |
|---|---|---|
| 2012 | 110 hp | R18Z1 |
| 2012 | 140 hp | R18Z1 |
| 2013 | 110 hp | R18Z1 |
| 2013 | 140 hp | R18Z1 |
| 2014 | 110 hp | R18Z1 |
| 2014 | 143 hp | R18Z1 |
| 2015 | 110 hp | R18Z1 |
| 2015 | 143 hp | R18Z1 |
1 factory vehicle, 2012–2015. Each year opens that model's engine table.