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Mercury 351 Cleveland V8 specs: 351 ci (5.8L) 8-cylinder, 4.00 x 3.50 in (101.6 x 88.9 mm) bore and stroke, 11:1 compression. Rated 300 hp. OHV.
The Mercury 351 Cleveland V8 is oversquare — the 4" bore exceeds the 3.5" stroke by 14.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.5" stroke puts mean piston speed at 4,000 ft/min around 6,850 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 43.9 ci (719 cc).
11:1 on iron heads is high enough that pump premium or better is normally required, and iron holds heat, so it is the less forgiving side of that line.
It is one of 2 engines in the 335 Series family, all of them 351 ci — the differences between them are in compression, heads and rating, not displacement. Factory fitments include the Mercury Cougar, Mercury Montego, Mercury Cougar Eliminator.
| Displacement | 351 ci / 5.8 L |
|---|---|
| Bore | 4" |
| Stroke | 3.5" |
| Cylinders | 8 |
| Compression ratio | 11:1 |
| Bore/stroke ratio | 1.143 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 300 hp |
| Bore/stroke character | 1.143 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,500 ft/min — conservative for a street engine |
| Displacement per cylinder | 43.9 ci |
| Static compression | 11:1 — high enough that pump premium or better is normally required |
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