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Mercury 200 specs: 200 ci (3.3L) 6-cylinder, 3.681 x 3.13 in (93.5 x 79.5 mm) bore and stroke, 8.5:1 compression. Rated 120 hp. Rod ratio and piston speed.
The Mercury Thriftpower Six (200) is oversquare — the 3.6811" bore exceeds the 3.1299" stroke by 17.6% — a layout that favors airflow and RPM over leverage at the crank. The 3.1299" stroke does not reach 4,000 ft/min of mean piston speed until about 7,650 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 33.3 ci (546 cc).
8.5:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 4 engines in the Thriftpower Six family, sitting between the 144 ci and 250 ci members. Factory fitments include the Comet, Zephyr, Capri and 5 others.
| Displacement | 200 ci / 3.3 L |
|---|---|
| Bore | 3.6811" |
| Stroke | 3.1299" |
| Cylinders | 6 |
| Compression ratio | 8.5:1 |
| Bore/stroke ratio | 1.176 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 120 hp |
| Bore/stroke character | 1.176 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,130 ft/min — conservative for a street engine |
| Displacement per cylinder | 33.3 ci |
| Static compression | 8.5:1 — low by modern standards, generally happy on regular pump fuel |
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