Bore, stroke, displacement and compression for all 4 Honda 120ci engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 119.5–120.4 ci |
|---|---|
| Cylinders | 4 |
| Bore | 3.189–3.307" |
| Stroke | 3.504–3.740" |
| Compression | 9.2–9.6:1 |
| Advertised power | 104–146 hp |
| Years | 1988–2001 |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| B20B | 120.4 ci | 3.3071" × 3.5039" | 9.2:1 | 126 |
| B20Z | 120.4 ci | 3.3071" × 3.5039" | 9.6:1 | 146 |
| B20A3 | 119.5 ci | 3.189" × 3.7402" | — | 104 |
| B20A5 | 119.5 ci | 3.189" × 3.7402" | — | 135 |
Both bore and stroke vary across the family, so these are separate castings rather than variations on one block.
All are undersquare — stroke larger than bore, favouring torque low in the range.
Each engine page carries rod ratio, mean piston speed, bore/stroke character and cylinder head specs where published, and links into the calculators with its dimensions already filled in.