differance between sd40-2 and gp40-2

[indian_hills_r_r]

I am looking at a couple engines. one is a sd40-2 the other is a Gp40-2. I am pretty sure the GP stands for General purpose. can someone tell me what the SD stands for. also what would be the  difference between the two.

[Len]

SD = Special Duty. Originally SD locos had 6 axles per truck to spread their weight out for operation on branch lines with lighter track and trestles and found on the mainline.

Len

[Terry Toenges]

I found this -
http://cs.trains.com/trn/f/111/p/160500/1768407.aspx

[Trainman203]

I read that link.  After 60 years, I still miss steam engines.  If you never saw them, you'll never get it.

  I heard someone once put it very well..... diesels are better than steam engines in every way except one -  the "cool factor."

[Len]

I read that link.  After 60 years, I still miss steam engines.  If you never saw them, you'll never get it.

  I heard someone once put it very well..... diesels are better than steam engines in every way except one -  the "cool factor."

And diesels are sneaky! After we moved from Missouri to New England, there were tracks running parallel to a road we used to walk on all the time. You could hear steam engines coming up behind you, so you had a chance to turn and wave. When the diesels came, they would creep up real quite like, and the first you knew they were there was when the horn went off and you jumped 3 feet straight up.

Len

[Piyer]

I am looking at a couple engines. one is a sd40-2 the other is a Gp40-2. I am pretty sure the GP stands for General purpose. can someone tell me what the SD stands for. also what would be the  difference between the two.

SD = Special Duty -- in many minds at the time of early diesel development, 4-axle locomotives were considered the norm, and anything with more (or less) was "special". The 6-axle units were developed for several reasons, but the original reasons were to spread out the tractive effort and / or weight. Except for passenger units (E-units) and the FL-9, all of EMD's 3-axle trucks had three powered axles. ALCO, on the other hand, produced 6-axle freight units in RSC (outer powered, middle idler) and RSD (all powered) variants.

As to the differences between an SD40-2 and GP40-2.... aside from the trucks and the frame length, the two models were basically the same beneath the hood. How they were used depends on the railroad in question. Rightly or wrongly, my personal rule of thumb is that Geeps were assigned to lighter,  faster, high priority trains, while the SDs were assigned to heavier, slower trains. There were and are exceptions to that - especially today where it seems that every train on the mainline is pulled by 6-axle units regardless of schedule. Refer to photos and other resources to see how your prototype or favorite railroad did / does things.

On a model railroad, the GP40-2 will take and look better on tighter curves than an SD40-2 will.

[Trainman203]

A steam engine to me is way cooler than anything else. Like I said, if you weren't  there in the day , you won't get it.