SD vs GP

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GPs have 2 axle trucks (4 wheels per truck) and SDs have 3 axle trucks (6 wheels per truck).
 


They are just EMD or GE model numbers. Some of them, like the SW-1200, indicated horsepower, but most are just internal company model numbers. I don't know the rhyme or reason for how they were chosen. For example, we have the GP-7 and GP-9. Whatever happened to the GP-8? Just one of life's mysteries. :)
 
Yes, to some extent. Number is approximate and is also rounded.

ES44DC/AC = 4400 horsepower
AC4400CW = 4400 horsepower
AC6000CW = 6250 horsepower
U9B - 1060 horsepower
U18B - 1800 hp
U23B/C - 2250 hp
The rest of the universal series follows the trend, then came the dash 7s
B23-7 - 2250 hp
The rest of the Dash 7s follow the trend.
Dash 8-32B - 3150 hp
Dash 8-32C - 3200 hp
BB40-8M (export model) - 4100 hp
The rest of the Dash 8s and Dash 9s follow the trend

There were also passenger locos.
U34CH - 3600 hp
P42DC - 4250 hp
The rest of the passenger locos follow the trend.

GE's domestic (non-export) electric locos all also follow the trend after the E44.

The only exception is the early switchers (44tonners, 45tonners, 70 ton switchers, etc) which reflect the weight of the locomotive which was a big deal back then due to some tax terms or weight restrictions (I am not entirely sure)
 
GE was consistent with the horepower matching the model number, or at least rounded up or down and close to the horsepower. The AC6000CW was the first major departure, with some units having 6350 HP and some having 4390 HP, but still the same model number. EMD only connected horepower to model numbers to switchers more or less consistently. There were some EMD road units, like the -18's, -20's, -24's and MP-15's where the model matched the horsepower but, after that, the model number had nothing to do with horsepower.

Edit: Di, you and I were posting at the same time. Good listing. The weight issue was due to union rules with the 44 tonners. Any engine of less than 45 tons only required and engineer. Anything 45 tons or over required an engineer and fireman. The 44 tonner was created to get around the two man crew rule. GE always described their engines by weight until the introduction of the U-boats.
 
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And...

"38" have 2 fan on the top

"40" have 3

"GP" mean General purpose and "SD" Service duty ( i'm not sure on this one)

GP38-2 = 4 axle and 2 fan
GP40-2 = 4 Axle and 3 fan

SD38-2 = 6 axle and 2 fan
SD40-2 = 6 Axle and 3 fan

Thanks !
 


diburning, the GE U34CH was only 3600 HP when the HEP generator was not running. Erie-Lackawanna liked to run a few U34CH's on freights to binghamton on weekends, not to the delight of the NJDOT. But when in HEP it ran at 3450HP.
 
Don't SD units tend to run more mainline than GP units? I always figured that GP's were the switchers of the modern day.
 
Steve, that's more true today but wasn't in the past. Geeps were common mainline units when horsepower ratings were lower than today's machine shops on wheels. :) The weight is better spread by a six axle trucks and the higher horsepower is also better untilized by the six wheel trucks. That brings up an interesting question though. Other than the MP-15, what was the last new B-B diesel produced for mainline freight service?
 
UP2CSX said:
Other than the MP-15, what was the last new B-B diesel produced for mainline freight service?
Click to expand...
B40-8W, and GP60M.
EMD briefly started a horsepower-oriented model numbering system starting with the GP18/SD18, and ending with the GP20/SD24. They moved back away from that when their new locomotive produced 2250 hp, versus the upstart GE locomotive's 2500 hp. Instead of a GP23, they went with GP30, just to make their number higher than GE's U25B.
Not that anybody asked, but EMD's usually shared common frame components. The GP38, GP39, and GP40 all shared the same frame. Same with the SD38, SD39, SD40, F45 and SD45. The "oddballs" were the SD40A, SDP45 and FP45, which shared a common frame that was longer than standard. This carried though the dash 2 era as well.
 
Terry, I thought the GP60M might have been the last B-B unit produced by EMD. I forgot about the B40-8W, although there were 83 B40-BW made in 1990, a year later than the last B40-8W. Since the GP60 was last produced in 1994, I guess that marks the last year for true road unit B-B production although some railroads use the GP20D as road units. It's interesting to have watched the transition over the years. The 60's and 70's were the B-B era in terms of numbers but I think the SD-40 was the beginning of the change to C-C's becoming common. It still looks odd to me not to see any B-B units outside of yards and local jobs. I can remember EMD marketing the SD-7/9's as a better alternative to the GP-7/9's but the Geeps outsold the SD's 8 to 1. Now the pendulum has swung completely to the side of C-C's.
 
After the sale of EMD, the company did not have a central production plant. That hampered the development and building of new locomotives such as anything beyond the GP60.

As the locomotives got larger, 6 axles became more common as Class 1s all wanted more power. Notice how GE hasn't built any 4 axle locomotives since the Dash 8s?

Right now, the switcher market is good because the MP15s were the end of mainsteam switcher production. Railroads began asking rebuilders to rebuild their second generation geeps to be switchers. EMD is making a killing from the ECO engine, and NRE is also doing very good with the gensets. (environmentally friendly switchers)
 
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