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7,000 horsepower: Jay Leno drives a Big Boy, the largest steam locomotive in the world

Let's go through the characters briefly before I tell you a little story about the magnificent colossus. The locomotive, including the tender, weighs 600 tons or 1.2 million pounds. The engine alone weighs 345,640 kg (762,000 lb), while the carbon-loaded unit weighs 193,210 kg (427,500 lb) (pun intended).

The math isn't right, is it? 1.2 million pounds equals 544 tons – at least that would be a quick conversion. But the Big Boy was made at a time when tons were not a generally accepted unit of mass, so we're dealing with 600 short tons (that's 544 metric tons), with a short ton being precisely defined as 2,000 lbs (907 kg). .

Back to the locomotive: 56,705.88 cubic inches of displacement (that's 929.25 liters, almost a cubic meter!), four cylinders, sixteen 68-inch/1,727 mm wheels – basically every hot rodder's wet dream. The engine alone is almost 86 feet (26 meters) long. Still, the locomotive is a massive 133 feet (41 meters) long from buffer to tender buffer. There is an infographic in the gallery that compares the Big Boy to various other modes of transportation.

Photo: YouTube/Jay Leno's Garage

Such a monster didn't just run with unicorn eyelashes and the tooth fairy's smile: at full throttle it burned 56,000 pounds (25.4 tons) of coal in two hours. 24,000 gallons of water evaporated. That's 91 tons (or cubic meters) of water converted into superheated steam at a pressure of 300 PSI. The gases would move the four pistons that drive the four sets of drive wheels.

In train parlance, this locomotive would be described as a 4-8-8-4 with four wheels at both ends (front and rear) and sixteen driving wheels that move the entire assembly consisting of locomotive, tender and freight car. Getting 670 tons of locomotive and around 4,000 tons of train moving from a standstill is not exactly easy – in both senses of the word – and requires a lot of preparation, as Jay Leno discovers during his ride on the Union Pacific 4014 Big Boy locomotive.

The hour-long video below briefly introduces the intricate workings of this gigantic engineering marvel from 1941. Given its complexity and sheer size, it is a veritable magic trick that it was built in less than a month in November 1941. Along with its nineteen sister, they were Big Boy class locomotives that entered service around the time America entered World War II.

1941 Union Pacific Big Boy steam locomotive

Photo: YouTube/Jay Leno's Garage

The nickname was a random joke, if you will, played by one of the American Locomotive Company's machinists at the assembly plant, who wrote the two words on the smokebox of the first Locomotive Company, serial number UP 4000. The name stuck: and I have to admit it's a lot catchier than what Union Pacific originally chose (“Wahsatch,' after a route along which the large machines were designed and built to operate).

The maximum power of the steam engines is around 6,290 hp or 6,377 hp (at least this power was reported in 1941, when low-grade coal from the Union Pacific mines was burned). And I said it right: “engines,” as in two of them. The Big Boys were essentially two steam engines working in tandem and mounted on a single articulated frame.

The current output is around 7,000 hp / 7,097 hp due to the boiler conversion to oil during the five-year restoration of the Big Boy 4014. Between 2014 and 2019, the heavy machine was dismantled, carefully inspected and carefully rebuilt to the same performance of its original specifications as deemed operationally feasible.

1941 Union Pacific Big Boy steam locomotive

Photo: YouTube/Jay Leno's Garage

The long project required enormous logistical effort and technical solutions to problems arising from the aging of the steam locomotive. In plain language: His parts were no longer available anywhere on Planet Piston. The last Big Boys were decommissioned in 1962. Without demand for replacement parts, there would be no manufacturer to produce them.

On July 20, 1959, a decade to the day before the moon landing, Union Pacific 4014 ended its 18 years of active service after 1,031,205 miles (1,659,564 kilometers). That's the equivalent of two round trips to the moon when the natural satellite is 252,088 miles (405,696 km) farthest from Earth. It was written off and donated to a museum in California in December 1961, two decades after it entered tax service.

It was a popular attraction at the Los Angeles County Fairgrounds from 1962 to 2014, when it was towed to Wyoming and underwent a major overhaul that returned it to service. However, unlike eight decades ago, vital raw materials and resources are transported throughout the country. Still, it serves as a tourist attraction for the company that originally commissioned it: Union Pacific.

1941 Union Pacific Big Boy steam locomotive

Photo: YouTube/Jay Leno's Garage

The historic locomotive has been equipped with a Positive Train Control (PCT) system to fully comply with 2024 rail transport standards and regulations. Basically, it is a computerized mechanism which makes it fully compatible with today's digital technology used in modern trains.

Regardless of the binary brains transplanted into it, the Big Boy needs four days to maintain the ice-cold pressure. Heating 25,000 gallons (94.6 cubic meters) of analog water with an old-fashioned fire still takes some time, but the locomotive doesn't take long rest periods between runs, so in most cases it takes less to get it running.

When the Big Boy 4014 completed its last sales trip in 1959, it went down in history. The year marked the centennial of the Golden Spike ride beginning in May 1859, when the east and west coasts of the United States were connected by railroad. The first transcontinental railroad, connecting the East Coast to the Pacific Coast, was completed on May 10, 1859.

1941 Union Pacific Big Boy steam locomotive

Photo: YouTube/Jay Leno's Garage

The large locomotives were designed by Union Pacific and built by ALCO (American Locomotive Company). The price of each unit was $265,174 in 1941, which is approximately $5,678,620 in 2024. A total of 25 Big Boys were put together in two production slots.

The first twenty units were built in 1941, while the remaining five were built in 1944. Eight of the super-heavy locomotives still exist today, but all are museum pieces, with the notable exception of 4014, the last surviving fossil from the purely analog era of our history.


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