Usually, with hood units, the 4 and 6 axle units had the same series number, like GP40 and SD40, up to the 60 series. However, there was the GP20 and SD24. Why the difference? And no SD30, right?
Original Post
Replies sorted oldest to newest
@Dominic Mazoch posted:Usually, with hood units, the 4 and 6 axle units had the same series number, like GP40 and SD40, up to the 60 series.
That was the "new era" of model designations which came after the GP30. Originally, the next turbocharged locomotive mode, after the SD24 & GP20, was going to be the "GP22", since it had 2250 horsepower. However, GE then came out with their U25B model, and the EMD General Sales Manager was not about to try and market a locomotive model with a number lower than a GE! Thus, the "GP22" became the GP30, and subsequent model numbers increased by "5", leading to the 35 series, the 40 series, the 45 series, the 50 series, and then the 60 series (with subsequent model number increases by '10').
However, there was the GP20 and SD24. Why the difference?
Because the SD24 was 2400 horsepower, while the GP20 was only 2000 horsepower.
And no SD30, right?
Correct. The "SD" model series did not return until the 35 series.
Also, at the time that the GP20 and SD24 came out EMD's traction motors could only handle about 500 HP each, so the GP20 was limited to 2000 HP, while the six motor SD24 could handle up to 3000 HP.
As for why SD30, the biggest reason was that at the time six motor units didn't sell anywhere as many as four motor units, so there was very little impetus to produce a six motor version of the GP30. Plus the marketing headaches of sell a 2250 HP GP30 and a 2400 HP SD30 as well.
Stuart
