by Allen Hazen
(((I think it is occasionally interesting to speculate about never-built, but posible, locomotive types: even that considering their likely characteristics, and the reasons for their non-appearance, can illuminate the history of real locomotives. In that spirit.... though this one seems a bit more speculative than some.)))
The EMD "SD55," which could have been introduced around 1980, is a six-axle roadswitcher, intended for heavy, fast, freight service, powered by a turbocharged 20-cylinder 645F engine. In other words, the model that would fill the gap in the proportionality
SD40:SD45::SD50:????.
Q1: What would its power have been? Since SD50, with the 16-645F engine, were built at 3500 and later 3600 hp, it is easy to imagine power outputs up to 4500. The SD45, however, had been conservatively rated, with a lower output per cylinder than the 16-cylinder SD40. Since the SD45 was rated at 120% of an SD40, and since the SD50, in the early part of its history, was rated at 3500, I'm going to guess 4200 hp for an SD55: the same as the SD45X test/demonstrator units of 1970/1971. [[QUESTION: Was the 20-645F built for stationary or marine use? And if so, at what rated power?]]
Q2: What would it look like? The SD45X gives a possible answer, but it might have been a bit more interesting. The 20 cylinder engine and the radiator needed for high horsepower eat up frame length: even with the radiator end of the hood extending so far back that the rear corner steps are ladder style, the SD45X had to be built to SDP45 length. And that's with the dynamic brakes in their less-than-optimal position over the engine. To save on length, EMD put the d.b.s there on the GP50, so maybe they would have on the SD55 as well, but if they had adopted the newer d.b. style of the SD50, the SD55 would have had to be longer. In 1980 the 80 foot length of the SD80/SD90 might have seemed to radical, but I'm going to ***guess*** at a 76 foot locomotive. ...
... Flared radiators would be a must if the length of the radiator compartment wasn't going to get out of hand. One way of saving a couple of feet would be to use larger fans (three 56inch fans would have the same swept area as four 48inch), but EMD might have been reluctant to deviate from their standard.
Q3: Why wasn't it built? This is the easy one: utter and total lack of customer demand. The last SD45-2 had been built in 1974. By the end of the 1970s some railroads were-- very tentatively-- beginning to investigate the possibilities for higher power, but the improved wheelslip control of EMD's 50-series (and GE's "Sentry" system introduced on later Dash-7) made some of them think that 4-axle units could replace the 1970s standard CC. (Most SD50 were built in 1983 or later: the GP50 outsold it early in the 50 series's history.) Finally, the U.S. was in a recession in the early 1980s (Conrail was able to make major locomotive purchases in 1983-1985 because the builders were desperate and offered super deals!): by the time the economy recovered, EMD had given up on the problematic 645F and introduced the 60 series with 710 engines (no 50 series units were built for U.S. railroads after 1985).
The EMD "SD55," which could have been introduced around 1980, is a six-axle roadswitcher, intended for heavy, fast, freight service, powered by a turbocharged 20-cylinder 645F engine. In other words, the model that would fill the gap in the proportionality
SD40:SD45::SD50:????.
Q1: What would its power have been? Since SD50, with the 16-645F engine, were built at 3500 and later 3600 hp, it is easy to imagine power outputs up to 4500. The SD45, however, had been conservatively rated, with a lower output per cylinder than the 16-cylinder SD40. Since the SD45 was rated at 120% of an SD40, and since the SD50, in the early part of its history, was rated at 3500, I'm going to guess 4200 hp for an SD55: the same as the SD45X test/demonstrator units of 1970/1971. [[QUESTION: Was the 20-645F built for stationary or marine use? And if so, at what rated power?]]
Q2: What would it look like? The SD45X gives a possible answer, but it might have been a bit more interesting. The 20 cylinder engine and the radiator needed for high horsepower eat up frame length: even with the radiator end of the hood extending so far back that the rear corner steps are ladder style, the SD45X had to be built to SDP45 length. And that's with the dynamic brakes in their less-than-optimal position over the engine. To save on length, EMD put the d.b.s there on the GP50, so maybe they would have on the SD55 as well, but if they had adopted the newer d.b. style of the SD50, the SD55 would have had to be longer. In 1980 the 80 foot length of the SD80/SD90 might have seemed to radical, but I'm going to ***guess*** at a 76 foot locomotive. ...
... Flared radiators would be a must if the length of the radiator compartment wasn't going to get out of hand. One way of saving a couple of feet would be to use larger fans (three 56inch fans would have the same swept area as four 48inch), but EMD might have been reluctant to deviate from their standard.
Q3: Why wasn't it built? This is the easy one: utter and total lack of customer demand. The last SD45-2 had been built in 1974. By the end of the 1970s some railroads were-- very tentatively-- beginning to investigate the possibilities for higher power, but the improved wheelslip control of EMD's 50-series (and GE's "Sentry" system introduced on later Dash-7) made some of them think that 4-axle units could replace the 1970s standard CC. (Most SD50 were built in 1983 or later: the GP50 outsold it early in the 50 series's history.) Finally, the U.S. was in a recession in the early 1980s (Conrail was able to make major locomotive purchases in 1983-1985 because the builders were desperate and offered super deals!): by the time the economy recovered, EMD had given up on the problematic 645F and introduced the 60 series with 710 engines (no 50 series units were built for U.S. railroads after 1985).