Buick 231ci specs: 3.80 x 3.40 in (96.5 x 86.4 mm) bore and stroke, shared by all 12 versions. Displacement, compression and factory ratings, plus rod ratio.
| Displacement | 231 ci |
|---|---|
| Cylinders | 6 |
| Bore | 3.800" |
| Stroke | 3.400" |
| Compression | 8.3–11.8:1 |
| Advertised power | 105–235 hp |
| Years | 1975–1999 |
| Cylinder head data | 1 of 12 engines |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| Buick 231ci · 3.800" × 3.400" · 9.321:1 | 231 ci | 3.8" × 3.4" | 9.321:1 | 115–170 |
| 1985 231 110HP | 231 ci | 3.8" × 3.4" | 8.391:1 | 110 |
| 1985 231 120HP | 231 ci | 3.8" × 3.4" | 8.39:1 | 120 |
| 1985 231 200HP | 231 ci | 3.8" × 3.4" | 8.3:1 | 200 |
| Buick 231ci · 3.800" × 3.400" · 9.5:1 | 231 ci | 3.8" × 3.4" | 9.5:1 | 150 |
| 1986 231 235HP | 231 ci | 3.8" × 3.4" | 8.4:1 | 235 |
| Buick 231ci · 3.800" × 3.400" · 9.8:1 | 231 ci | 3.8" × 3.4" | 9.8:1 | 165–205 |
| 1993 231 170HP | 231 ci | 3.8" × 3.4" | 10.3:1 | 170 |
| Buick 231ci · 3.800" × 3.400" · 11.8:1 | 231 ci | 3.8" × 3.4" | 11.8:1 | 195–205 |
| Buick 231ci (1975–1977) | 231 ci | 3.8" × 3.4" | — | 105–110 |
| LC8 | 231 ci | 3.8" × 3.4" | — | 150–180 |
| LM9 | 231 ci | 3.8" × 3.4" | — | 200 |
Compression spans 8.3:1 to 11.8:1, so fuel requirements differ meaningfully between members — worth checking before assuming parts interchange.
All are oversquare — bore larger than stroke, which favours revs over low-end torque.
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.