How Much Horsepower Is Too Much?

In the early days of Steam, and even in the first 30 years of Diesel-Electric locomotives, the challenge for any manufacture of locomotives was to get as much horsepower out of a single unit as possible.  The Horsepower Race for Steam Locomotives fizzled out when Diesel-Electrics started proving their worth during World War II.

One of the biggest selling point for 2nd and 3rd generation diesel-electrics was unit reduction.  Each unit could produce more horsepower then a previous generation of diesel-electrics, and thusly you needed fewer units to move a train.  This worked out well.  As an example:

• In 1962, 6 F unit locomotives could be used together to provide power up to 9,000 horsepower.


• In 1963, The same railroad company bought some GP30’s and used only four GP30’s to produce 9,000 horsepower.


• In 1966, The same railroad company bought some SD40’s and used three per train to produce 9,000 horsepower.

Union Pacific was always ahead of the class in terms of horsepower.  In the 1940’s it produced the 4-8-8-4 Big Boy Steam Locomotive, which was the worlds largest steam locomotive.  Not to be unmatched, it led the race with Diesels as well – often using some unique methods.  One of those methods was to use a Steam-Turbine-Electric system to power a diesel-esque looking locomotive with 2,500 horsepower, which was remarkable in 1939 when they made this happen.  In 1948 the UP used jet engine technology to create a 4,500 horsepower Gas-Turbine-Electric.

In 1958 UP teamed up with GE and created 10 ‘Big Blow’ locomotives, capable of 10,000 horsepower.  These were also Gas-Turbine-Electrics.  The UP was wild about horsepower, and in the 60’s it got Alco, GE and EMD all racing to build the UP the most powerful articulated locomotive possible.   Everyone was reaching for 15,000 horsepower.  EMD in theory won that race, with the DDA40X.  While They didn’t meet the goal, they did pretty darned good for a Diesel-Electric, pumping out 6,600 horsepower per twin engine unit.  Still the most powerful Diesel-Electric single unit locomotive ever produced.

AC Traction was the next biggest thing to come to the Diesel-Electric world.   Of course, AC Traction motors have been around for a long time,  and were known to be very efficient.  The problem was they liked to settle at whatever frequency the AC power was being provided at.  This meant that they were harder to control.  This is where computers came into play, and in the 1980’s this technology was readily available and caused a slew of AC Diesel Electrics to show up on the railroads.

AC Versions of Locomotives were often a few hundred horsepower more then their DC Counterparts.  For example, the SD70M is rated at 4,000 horsepower, while the SD70MAC is rated at about 4,300 horsepower.  EMD built a new engine to be used on AC units called the 265H which was a four cycle engine which could produce in-itself 6,000 horsepower.  This engine was an option in the new SD90MAC.  However only about 40 SD90MAC’s were produced with this new powerplant.

The reason being was that in the late 1990’s many railroads had came to realize that these 6,000 horsepower units were a waste.  Most heavy unit trains these days require a total of 12,000 or so horsepower.  If you are using two 6,000 horsepower locomotives, and one breaks down, you will not have enough power to move that train with just one locomotive.  However with 3 locomotives rated at 4,000 horsepower, chances are you will still have just enough juice to continue to your destination.

AC Traction motors and 4 cycle engines are still being used, however these days not in an effort to win any horsepower races, but more so to reduce fuel consumption.  The GEVO-12 by GE is capable of producing 4,400 horsepower from 12 cylinders.  This is a big improvement to the previous standard engine that GE used to use, which was a 16 cylinder engine, which produced about the same amount of power.

Today the ideal horsepower rating for a single locomotive has been set at around 4,300 horsepower.  And the new race is to reduce fuel consumption and to create ‘greener’ locomotives.