Bore, stroke, displacement and compression for all 10 Mercury Cologne engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 170–256 ci |
|---|---|
| Cylinders | 6 |
| Bore | 3.661–3.953" |
| Stroke | 2.697–3.500" |
| Compression | 8.7–9.7:1 |
| Advertised power | 101–210 hp |
| Years | 1961–2011 |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| 256 | 256 ci | 3.9528" × 3.5" | 9:1 | 205 |
| 255 | 255 ci | 3.9528" × 3.5" | 9:1 | 145 |
| 4.0 SOHC | 245 ci | 3.9528" × 3.3228" | 9.7:1 | 210 |
| Cologne 4.0 OHV | 245 ci | 3.9528" × 3.3228" | — | 155–160 |
| 4.0 SOHC | 245 ci | 3.9528" × 3.3228" | — | 205–210 |
| 4.0 SOHC Cologne | 245 ci | 3.9528" × 3.3228" | — | 210 |
| Cologne OHV V6 EFI | 245 ci | 3.9528" × 3.3228" | — | 160 |
| Cologne SOHC V6 | 245 ci | 3.9528" × 3.3228" | — | 207 |
| 2.8L V6 | 170 ci | 3.6614" × 2.6969" | 8.7:1 | 109 |
| Cologne (1961–1963) | 170 ci | 3.6614" × 2.6969" | — | 101 |
Both bore and stroke vary across the family, so these are separate castings rather than variations on one block.
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.