Mercury 428 Cobra JET V8 Specs

Mercury 428 Cobra JET V8 engine specs: 428 ci (7L), 8-cylinder, 4.1299" bore x 3.7874" stroke, 10.6:1 compression.

Dimensions

Displacement428 ci / 7 L
Bore4.1299"
Stroke3.7874"
Cylinders8
Compression ratio10.6:1
Bore/stroke ratio1.09

Construction

Block materialcast iron
Head materialcast iron
ValvetrainOHV
Fuel typegas
Advertised HP335 hp

What these numbers mean

Bore/stroke character1.090 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves
Mean piston speed at 6,000 RPM3,787 ft/min — in the range typical of performance street engines
Displacement per cylinder53.5 ci
Static compression10.6:1 — in the range that usually runs on pump premium

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