The Packard 4M-2500 engine was utilized in all U.S. Navy World War II PT boats. This engine was based on the 1925 Liberty aircraft engine which was earlier converted for marine use in racing boats. During the war the Packard engine went through various performance updates and modifications. With early engines rated at 1100 h.p. and progressing to 1500 h.p. during the war. The Packard 4M-2500 engine was a supercharged, water cooled, gasoline powered V-12 engine, weighing approximately 2900 pounds.

The Packard 4M-2500 marine engine was not the Rolls-Royce Merlin, nor did U.S. Navy PT boats use the R.R. Merlin engines, which is sometimes misstated. However, Packard did built a version of Merlin Engine under contract by Britain for British aircraft use.

Packard 4M-2500, Super Charged V-12 Gasoline Marine Engine

 The Packard 4M- 2500 - PT Boat Engine
Cylinders: 12 - V angled arrangement
Supercharger: Gear driven - centrifugal
Cooling:  Fresh water
Maximum RPM: 2400 rpm, 2000 rpm sustained
Rating: 1200, 1350, 1500 depending on year of manufacturing
Fuel: 100 Octane gasoline
Fuel Consumption
at 40 knots:
Top speed at 40 knots, running three engines, 474 gallons per hour. Full fuel load (3,000 gallons) 6.3 hours.
Fuel Consumption
at 40 knots:
Maximum sustained speed at 2000 rpm, running three engines, 292 gallons per hour. Full fuel load (3,000 gallons) 10.3 hours, range radius of 259 miles at 35 knots, 518 miles total.


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Tel: (901) 755-8440 , Fax: (901) 751-0522

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This site was last updated 10//17/2003