posted
Generally speaking, a GP will have 4 axles, while an SD will have 6. The GP40 & SD40 are both rated at 3000 hp, just that the only major difference is the number of axles.
[This message has been edited by CG96 (edited 09-13-2003).]
posted
It is interesting that although SD's are larger than GP's, they are not anymore powerful than their counterpart. SD's are typically used for branch lines and areas that have lighter rail, or less routine maintenance. The three axles on each truck spread the weight out, so the track does not have to be as strong to support them.
quote:Originally posted by Konstantin: It is interesting that although SD's are larger than GP's, they are not anymore powerful than their counterpart. SD's are typically used for branch lines and areas that have lighter rail, or less routine maintenance. The three axles on each truck spread the weight out, so the track does not have to be as strong to support them.
Actually that is not quite acurate. Some of the early six axle locomotives had two powered axles with a dummy idler axle on each truck to spread the load on light branch lines, but by the time the Gp40 & Sd40 came out, both were intended as high horsepower road power. I think the Sd40 would have more tractive effort available than a Gp40 even though the prime mover was rated at the same horsepower, because it has six traction motors compared to four in the gp. In the 60's when the Gp40 and Sd40 came out the gp would probably run at higher speeds while the sd might be used more for slow drags. Today, virtually all new power is six axle. I don't think anyone has made four axle power units since the Gp60's and Dash8 40b's of the 90's, with the exception of the new Amtrak power units.
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