Whats the Difference?

What is the difference between an SD9 and a GP9?

HA-Ha, ya got me, on that one, James.... Too funny. But seriously, as an "engineer", you should know, that the "GP", or General Purpose series of locomotives, have 4 axles. The SD, or Super Duty series, are six axles. Look harder at all those HO trains you have, and start counting axles.......

OK, I thought that there was a differance in the prime movers, as well as the maximum load each can carry.....

Not just the Axles....

Both the GP9 and the SD9 used the 16V-567C engine. Obviously with two additional axles the SD9 could drag 50% more tonnage than a GP9 could.

I don't believe the SD could pull 50% more - the peak horsepower output is the same, just distributed to 6 axles rather than 4. I'm sure someone here has specific figures on tractive effort they will share with us.

Goldon Arm, man that was like lookin at last weeks math test.....

Ok, so 50% more than a GP9? Well, then really 6 axles make a difference eh?

Well, although I think Golden-Arm has covered this mostly, I might add a couple points;

First, James, anytime you see two EMD locomotives of type "GP" and "SD" they will have the same engine. Note that there are GP units with no SD equivalent, and vice versa, and naturally this ONLY applies to GP and SD designations (and thus not SW, E or anything else.)

Second, we can look at continuous ratings. EMD itself did not assign a short-time rating to the GP-9 since it felt that adhesion would prevent the locomotive from overloading, but the railroads did use a common figure for the GP-9 for minimum continuous speed and corresponding effort. (Using PRR figures.)

GP-9: 44,600 lbs @ 11.8 MPH
SD-9 67,000 LBS @ 7.0 MPH

As we can see, the SD does in fact have roughly half again as much continuous effort (logical and in fact obvious when comparing four vs six identical motors with the same gear ratio) but since the engine is the same it achieves this 50% greater effort at a much lower speed.

Now let's compare locomotive weights and starting tractive efforts at 25% adhesion (using PRR units):

GP-9: 249,000 LBS / 62,250 LBS STE
SD-9: 356,000 LBS / 89,000 LBS STE

So, then, the SD-9 as compared here did in fact have 50% greater continuous effort and approximately 50% greater starting tractive effort than the GP-9.

This relationship holds for other manufacturers' locomotives as well; look at some roughly contemporary ALCO-GE ratings.

RS-3 52,500 lbs continuous / RSD-5 78,750 lbs continuous / both units rated 13,125 lbs continous effort per driving axle.

Hope this helps with your four vs. six axle comparisons, James!

-Will Davis

GOLDEN-ARM wrote:HA-Ha, ya got me, on that one, James.... Too funny. But seriously, as an "engineer", you should know, that the "GP", or General Purpose series of locomotives, have 4 axles. The SD, or Super Duty series, are six axles. Look harder at all those HO trains you have, and start counting axles.......

When the SD7 and SD9 were introduced they were advertised as being Special Duty locomotives for light rail branches.

Just like the names for locomotives that GM used such as FT for "F"ifty four hundred horsepower for 4 units or "T"wenty seven hundred horsepower for two units, then later F for "F"ifteen hundred horsepower, and SW as "S"ix hundred horsepower "W"elded frame, when the locomotive horsepower began to exceed the original names, the marketing department came up with new names for the same letters and did everything they could to erase what the letters were meant to stand for.

Interesting, you learn something new everyday...

Some information
http://en.wikipedia.org/wiki/GP9
and more.
http://en.wikipedia.org/wiki/EMD_SD9

U-Haul wrote:Some information
http://en.wikipedia.org/wiki/GP9
and more.
http://en.wikipedia.org/wiki/EMD_SD9

I would sooner point someone in the direction of the National Inquirer, than the Wikki. Really.

Golden Arm I am going to have to completely disagree with you on your Wikipedia comment. Wikipedia is a working encyclopedia and has made great strides in its accuracy and content at least in the realm of locomotive history. Wikipedia is only as good as the people who write and edit for it. BTW you spelled Enquirer wrong!

GOLDEN-ARM wrote:

U-Haul wrote:Some information
http://en.wikipedia.org/wiki/GP9
and more.
http://en.wikipedia.org/wiki/EMD_SD9

I would sooner point someone in the direction of the National Inquirer, than the Wikki. Really.

And if submit something false there, and so do you, and we "enlist" a third person to back our claim, then our "fact" becomes that, in the Wiki. Thanks for that spelling lesson. I was too busy, in school, learning how to operate locomotives, and didn't have time for homework, or serious studies. You can bank on the Wiki, if you want. I will settle for the facts.

GOLDEN-ARM wrote:

U-Haul wrote:Some information
http://en.wikipedia.org/wiki/GP9
and more.
http://en.wikipedia.org/wiki/EMD_SD9

I would sooner point someone in the direction of the National Inquirer, than the Wikki. Really.

If you've got a problem with something on Wikipedia, you're always free to change it. That's the beauty of it.

I've fixed up several wikipedia articles that were full of baloney. It's kinda fun.