nhl jerseys with laces 2500 engine in detail
No, it’s not a Merlin. Even though Packard produced Rolls Royce Merlins under licence during the Second World War Two, the 4M 2500 is an altogether different kettle of fish. It was designed before the war by Jesse Vincent, Packard’s chief engineer, for use in the US Navy’s new motor torpedo boats built by Higgins and Elco. Vincent favoured the V12 configuration because of its inherent balance and refinement as well as its power potential. The 3.5 litre pistons were as big as coffee tins the name stuck.
“It’s the sort of engine that can suck your shirt out of your trousers,” says Williams, quoting an American lake racer who in 1929 had a boat with four Packard engines installed.
Weighing 2,900lb, the 41.8 litre, four stroke, V12 4M 2500 had a single overhead cam per bank, with four valves and two spark plugs per cylinder. It fired through a four pole magneto ignition and the massive centrifugal supercharger sat in front of the engine, with inlet charge cooling on later versions. It breathed through a Holley 1685F aeroplane carburettor that used giant diaphragms to counteract different air pressures and inverted operation.
“We try not to do inverted operation,” says Williams.
Running on aviation quality 100 octane fuel, the first engines developed 1,200bhp but later, improved versions with higher boost levels made 1,650bhp. Packard built 14,000 marine engines during the war on East Grand Avenue, Detroit and the US navy’s 768 PT boats were fitted with three of them, two astern and one amidships for ease of servicing.
“Men bet their lives on it,” said Packard’s engine publicity. They certainly did. These fragile, plywood hulled craft weighed 50 tons when armed with torpedos and machine guns, mustered 4,500bhp and they carried their crews into battle with Japanese men of war and merchant ships. Doing 50 knots (42mph) at full chat, the engine’s wolfed down 500 gallons of juice an hour. Crews would approach fast, let go the torpedos and then turned just as the enemy realised what was going on and opened up with everything it had.
The engines had an overspeed cutout which, by legend, was hammered off on these pell mell escapes so these to extraordinary engines were let free to rev up to and beyond 2,400rpm. By all accounts it was quite a sight. You need to see John Ford’s 1945 film They Were Expendable, or read US president John F. Kennedy’s memoir PT 109 he was awarded the Navy and Marine Corps Medal for his heroism in helping his crew to safety after his PT boat was rammed and sunk by a Japanese destroyer.
What’s more, the crews would tune them up. After an exercise, the PT boats would race back to base, the lead boat crossing the others, its wake soaking the crews. Setting up the dual ignition points correctly was vital to avoiding giving your skipper a soaking and there are even stories of scrolling up the supercharger drives.
These days any engines that still exist are mostly scrap, although after the war several record breakers used them in boats. Packard engines had gained a great reputation for reliable power before the war with prohibition bootleggers as well as more bone fide Great Lakes racers like Gar Wood who, with Jesse Vincent’s help, fitted Packard Liberty engines to his Miss America boats for the famous series of Gold Cup races.