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Mercury 170 specs: 170 ci (2.8L) 6-cylinder, 3.50 x 2.94 in (88.9 x 74.7 mm) bore and stroke, 9.1:1 compression. Rated 101 hp. Rod ratio and piston speed.
The Mercury Thriftpower (170) is oversquare — the 3.5" bore exceeds the 2.94" stroke by 19.0% — a layout that favors airflow and RPM over leverage at the crank. The 2.94" stroke does not reach 4,000 ft/min of mean piston speed until about 8,150 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 28.3 ci (464 cc).
9.1:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 5 engines in the Thriftpower family, sitting between the 144 ci and 250 ci members. Factory fitments include the Mercury Comet, Mercury Montego.
| Displacement | 170 ci / 2.8 L |
|---|---|
| Bore | 3.5" |
| Stroke | 2.94" |
| Cylinders | 6 |
| Compression ratio | 9.1:1 |
| Bore/stroke ratio | 1.19 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 101 hp |
| Bore/stroke character | 1.190 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,940 ft/min — conservative for a street engine |
| Displacement per cylinder | 28.3 ci |
| Static compression | 9.1:1 — low by modern standards, generally happy on regular pump fuel |
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