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Mercury 427 SOHC specs: 427 ci (7.0L) 8-cylinder, 4.228 x 3.787 in (107.4 x 96.2 mm) bore and stroke, 12:1 compression. Rated 610 hp. SOHC.
The Mercury 427 SOHC is oversquare — the 4.2283" bore exceeds the 3.7874" stroke by 11.6% — a layout that favors airflow and RPM over leverage at the crank. The 3.7874" stroke puts mean piston speed at 4,000 ft/min around 6,350 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 53.4 ci (875 cc).
12:1 on iron heads is high for a production gasoline engine; running a ratio like that on pump fuel depends on chamber design and fuel delivery rather than the number alone.
It is one of 34 engines in the FE family, sitting between the 332 ci and 428 ci members. Factory fitments include the Mercury Comet, Mercury Comet (drag racing).
| Displacement | 427 ci / 7 L |
|---|---|
| Bore | 4.2283" |
| Stroke | 3.7874" |
| Cylinders | 8 |
| Compression ratio | 12:1 |
| Bore/stroke ratio | 1.116 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | SOHC |
| Fuel type | gas |
| Advertised HP | 610 hp |
| Bore/stroke character | 1.116 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,787 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 53.4 ci |
| Static compression | 12:1 — high enough that pump premium or better is normally required |
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