Bore, stroke, displacement and compression for all 5 Hyundai Theta II engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 121.9–146.5 ci |
|---|---|
| Cylinders | 4 |
| Bore | 3.386–3.465" |
| Stroke | 3.386–3.819" |
| Compression | 9.5–11.3:1 |
| Advertised power | 175–274 hp |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| G4KC | 146.5 ci | 3.4646" × 3.8189" | 11.3:1 | 190 |
| Theta II · 3.465" × 3.819" · 10.5:1 | 144 ci | 3.4646" × 3.8189" | 10.5:1 | 175–178 |
| Theta II · 3.465" × 3.819" · 11.3:1 | 144 ci | 3.4646" × 3.8189" | 11.3:1 | 185–190 |
| Theta II · 3.386" × 3.386" · 10:1 | 121.9 ci | 3.3858" × 3.3858" | 10:1 | 245–274 |
| G4KH 20T | 121.9 ci | 3.3858" × 3.3858" | 9.5:1 | 274 |
Both bore and stroke vary across the family, so these are separate castings rather than variations on one block.
Compression spans 9.5:1 to 11.3:1, so fuel requirements differ meaningfully between members — worth checking before assuming parts interchange.
3 of 5 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.