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Mercury 144 specs: 144 ci (2.4L) 6-cylinder, 3.50 x 2.50 in (88.9 x 63.5 mm) bore and stroke, 8.7:1 compression. Rated 90 hp. OHV. Rod ratio and piston speed.
The Mercury Thriftpower (144) is oversquare — the 3.5" bore exceeds the 2.5" stroke by 40.0% — a layout that favors airflow and RPM over leverage at the crank. The 2.5" stroke does not reach 4,000 ft/min of mean piston speed until about 9,600 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 24.0 ci (393 cc).
8.7:1 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, the smallest at 144 ci. Factory fitments include the Mercury Comet.
| Displacement | 144 ci / 2.4 L |
|---|---|
| Bore | 3.5" |
| Stroke | 2.5" |
| Cylinders | 6 |
| Compression ratio | 8.7:1 |
| Bore/stroke ratio | 1.4 |
| Piston deck clearance | 0.012" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 90 hp |
| Bore/stroke character | 1.400 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,500 ft/min — conservative for a street engine |
| Displacement per cylinder | 24.0 ci |
| Static compression | 8.7:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.467" |
|---|---|
| Exhaust valve diameter | 1.266" |
| Chamber volume | 43.6 cc |
| Rocker ratio | 1.5:1 |
| Lifter type | hydraulic |
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