Hi, maybe Im just dumb, but whats the physical difference between GP7 and GP9?\
Thanks
According to original “Diesel Spotters Guide” on pg. EMD-25, “The GP-7 has three or four louvers below the cab and two vertical rows of louvers under the radiator shutters at the far end of the long hood. The GP-9 has one or no louver beneath the cab, and lacks the two vertical rows under the radiator shutters. Presence or absence of the dynamic brake blister tells nothing, as both GP-7’s and GP-9’s came with or without dynamic brakes.”.
Also on later Phases of the GP9 the 4 36" Radiator Fans became 2 - 48" Fans, and after many railroad modifications all spotting differences may become moot points.
Rick J
We wuz all dumb, once. Then we learned stuff. Frequently by asking.
I am assuming, when you use the word “physical”, that you mean “what you can see by looking at it from the outside”. Because there are also physical differences on the inside. Which don’t mean a whole lot to modelers.
And, frequently, as Rick just implied/noted above, there are subgroups of “physical”, called phases. And there can even be subgroups in those subgroups.
There are various resources that discuss phases, both on-line and bookish. One of my favorites (though it doesn’t have GP7/9’s) is:
http://www.trainweb.org/jaydeet/rosters.htm
Ed
Ed
I typed complete answers twice. Just as I was about to hit “submit”, a response was posted by somebody else and my post disappeared.
Briefly, look at pictures. Take note of the shape of the side sill (plain on GP7’s; shaped differently on late GP9’s), the presence or absence of slots in it (present on early GP9’s), and the locations and numbers of louvres in the hood sides and grille sides (more of them on GP9’s). The louvres under the cab, mentioned by Rick, don’t seem to be a consistent feature. I see them on photos of B&O GP7’s, but not on NKP GP7’s.
GP7’s used 36" roof fans. By the end of GP9 production, all roof fans were 48" diameter.
Dynamic brakes, “torpedo tube” air tanks, etc. are irrelevant, as they were options available on both models.
The GP7 produced 1500 h.p., and the successor GP9 produced 1750 h.p.
Tom
P.S.: No, Charles, you’re not dumb. The wide-body BB Athearn “GP9” was on the market for about 20 years before some eagle-eye realized it was a GP7. This was about the time that Tony Koester and others opened the eyes of many of us and began to promote the idea of better accuracy.
P.P.S.: I managed to get all the material posted by posting a short item, then adding to it with edits. Frustrating.
Also, ACY, if I recall, wasn’t the original Athearn SW 1500 actually SW 7 or something like that?
It was pretty much an early SW7 body with a late SW7 cab.
Ed
The only dumb questionsc are ones you don’t ask.
As I understand it, as delivered the access to the class lights and roof are individual rungs attached directly to the hood ends on most GP and SD-7’s and fabricated ladders on stand offs from the ends on GP and SD 9’s. This could be changed in the 50 to 60 years since.
The difference between a GP-7 and a GP-9?
runs like hell
The ladder thing is definitely not correct. Both SD7 and SD9 models had ladders instead of grabs, but I’ve never seen either a GP7 or GP9 with full ladders instead of grab irons.
The visual differences are all about the car body louvers, as described in one of the first responses here.
I’m trying to remember where I read this - I think one of my Northern Pacific books? I’ll try to track it down…Anyway, I remember reading that the frame of the GP-7 wasn’t all that strong. Something about the way it was welded - or that it was welded, rather than cast? Whatever it was, the GP-9 frame was stronger and more durable. I know GP-9s could last a long time, some of the Soo Line’s high nose GP-9s lasted long enough to get the all-red CP paint in the 1990’s.
Couldn’t all the differences listed be the way they were ordered by the railroads?
On GP7/9’s, louvres and side sill configurations were determined by EMD.
Options such as dynamic brakes, “torpedo tube” air tanks, steam generators, horns, Mars lights, and fuel tank capacity would have been determined by the purchaser.
Tom
And size and placement of radiator fans!
Rick J
GP7, GP9, GP18 The main differences were internal not external.
The most visible difference is the size and number of radiator fans (excluding the optional dynamic brake fan) but the GP7 and early GP9 had the same fans, that is 4 small fans. Latter GP9 had two larger fans. The GP18 also had two fans but they stuck up above the roof and had a shroud around them whereas the GP-9 fans were almost flush with the roof. However very late GP9 had the same fans as the GP18.
Louvers below the cab is often said to be the most reliable way to tell a GP9 from a GP7. The GP9 had the louvers the GP7 didn’t. But ACY stated, from his observation, that may not be true.
The arangement of the louvers on the long hood doors also varied over the production run GP7 through GP18.
Also with repairs, modifications and rebuilds parts got mixed.
The easyist and probably most reliable way to determine if a loco in a photo is a GP7, GP9 or GP18 is to note the locomotive number on the cab and check the railroads roster.
There was also the turbocharged GP20 which could easily be mistaken for a GP7, 9 or 18 from most angles. It had the same radiator fans as the GP18. The distinguishing feature was a tall louvered box on the long hood behind the cab.
Thankyou everyone for the replies!
So the biggest/only diffference is the louvers under the cab, got it!
Thanks [:D]
Charles
No, the biggest and most reliable difference is the two vertical lines of louvers towards the rear of the long hood, as on the old BB Athearn GP. The early GP9s also had the louvers under the cab.
Also remember that the railroads occasionally switched parts around during shopping, so you could sometimes end up with spotting features from different phases on a single unit.
John
Re my earlier post, this is what I was referencing:
“The major weakness of the GP-7 was it’s relatively light frame…in later years the frames would sag slightly in the middle. If the locomotive was used in road service where it operated with other units on heavy trains, its end platforms tended to bend down because of heavy buffeting.” (“Northern Pacific Diesel Era” Frey & Shrenk)
I don’t know that this would be really noticeable on a model, but would be interesting to try. Anyway, apparently the GP-9 had a stronger frame and didn’t have this problem.
As anyone who has tried to convert an Atlas/Kato GP7 to a GP9 has discovered:
The GP7 has a batten strip (a shallow channel with bolt heads or rivets) running up and over the long hood, before or after the location of the dynamic brake hatch.
I find the presence or absence of the batten strip a much more reliable guide than louvers that appear on hinged and detachable access panels.
It depends on when the locomotive was built. Drawings on this site: http://trainiax.net/mephoto.php
Show no difference in this respect between GP7 and early GP9. They have a identical continous narrow section or batten strip from the walkway over the top on both ends of the dynamic back location. The doors are the same but the louver placements are different. This, however may may not be a definitive difference…
The GP9 (phase 2, - 36" fans) and GP9 (Phase 3, - 48" fans) are different. They have no batten strip. There are narrow sections over the top but they do not go below the bottom of the dynamic brake panel on each side. There is no narrow section on the side behind the dynamic brake. There is a narrow section for hinges between doors on the side in front of the dynamic brake but it is separate from the section over the top. The first door behind the cab is hinged on the opposite side from the early GP9/GP7 and the louver pattern is different.
Bottom line:
Refer to photos for all modeling projects. The more photos, the more angles, the better.
Tom