Bore, stroke, displacement and compression for all 4 Mercury Thriftpower Six engines, compared side by side. Plus rod ratio and head specs where published.
| Displacement | 144–250 ci |
|---|---|
| Cylinders | 6 |
| Bore | 3.500–3.681" |
| Stroke | 2.500–3.909" |
| Compression | 8.5–9.0:1 |
| Advertised power | 85–155 hp |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| 250 | 250 ci | 3.6811" × 3.9094" | 9:1 | 155 |
| 200 | 200 ci | 3.6811" × 3.1299" | 8.5:1 | 120 |
| 170 | 170 ci | 3.5" × 2.9409" | 8.7:1 | 101 |
| 144 | 144 ci | 3.5" × 2.5" | 8.7:1 | 85 |
Both bore and stroke vary across the family, so these are separate castings rather than variations on one block.
The family mixes oversquare and undersquare designs, so members behave quite differently despite sharing a name.
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.