1A-2500
A preserved Packard 3A-2500 on display at the National Museum of the United States Air Force
Type	Liquid-cooled V12 engine
National origin	United States
Manufacturer	Packard
First run	1924
Number built	258

The Packard 1A-2500 is an American V-12 liquid-cooled aircraft engine designed by Packard in 1924 as a successor to the World War I-era Liberty L-12.^[1] Five aero variants were produced, of which the 3A-2500 was the most numerous. Three marine versions, used most prominently in American World War II PT-boats, the 3M-2500, 4M-2500, and 5M-2500, were also derived from it.^{[citation needed]}

Applications

• Boeing TB
• Heinkel HE 8
• Martin T3M
• Naval Aircraft Factory PN
• Huff-Daland LB-1
• PT boats - marine versions of the 3M/4M/5M-2500^{[citation needed]}
• Packard-Bentley one-off race car
• USSR World War II torpedo boats and sub-chasers, which were fitted with 535 4M-2500 engines with W-8 modification under Lend-Lease^{[citation needed]}

Variants

1A-2500

1924, 800 hp. Six built.

2A-2500

1925, 800 hp. 75 built.

2A-2540

? Huff-Daland XHB-1

3A-2500

1926, Geared propeller drive option, 800 hp. 175 built.

4A-2500

1927, fitted with a supercharger, 900 hp. One built.

5A-2500

1930, experimental use only, 1500 hp. One built.

3M-2500

Marine version^{[citation needed]}

4M-2500

Marine version, 1200 hp (895 kW), subsequently upgraded in stages to 1500 hp (1,150 kW).^{[citation needed]}

5M-2500

Marine version, larger supercharger, aftercooler, and power output of 1850 hp^{[citation needed]}

Engines on display

• A Packard 3A-2500 is on display at the National Museum of the United States Air Force.^[2]
• A Packard 3A-2500 is in storage at the National Air and Space Museum.^[3]
• A Packard 3A-2500 is on display at the New England Air Museum.^[4]
• A Packard 4M-2500 is on display at the Packard Proving Grounds Historical Site in Shelby Twp., Michigan.^{[citation needed]}
• A Packard Series 142 Diesel Model 1D-1700 is on display at the Packard Proving Grounds Historical Site in Shelby Twp., Michigan.^{[citation needed]}
• Three working Packard 5M-2500s are installed the only operational PT boat, Higgins PT-658 in Portland, Oregon.^{[citation needed]}

Specifications (1A-2500)

Data from Aircraft Engine Historical Society^[5] and Race With the Wind By Birch Matthews^{[citation needed]}

General characteristics

• Type: 12-cylinder V engine
• Bore: 6+3⁄8 in (162 mm)
• Stroke: 6+1⁄2 in (165 mm)
• Displacement: 2,540 cu in (41.6 L)
• Dry weight: 1,120 lb (510 kg)

Components

• Valvetrain: Four valves per cylinder, overhead camshaft
• Fuel type: Petrol
• Cooling system: Liquid-cooled

Performance

• Power output: 850 hp (630 kW) at 2,500 rpm
• Specific power: 0.33 hp/in³ (15.2 kW/L)
• Power-to-weight ratio: 0.76 hp/lb (1.25 kW/kg)