Matt Farnsworth Wrote:
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> the space above the fuel tank where the air tanks normally go was used for water tanks.

Matt:
The air tanks located ABOVE the fuel tanks (and below the frame) did not come into practice until the GP20, which still had the basic body style of the GP7/GP9/GP18. Notice air tank placement in this picture of GP20 3043, ex ATSF (originally 1143, then 3143, finally 3043).



I am not aware of any GP20's built with steam generators for passenger service.

The picture below of GP7 NIWX 1617 (ex BN 1617 exx CB&Q 261) shows the "standard" air reservoir placement, on the long hood end of the fuel tanks, for "normal" configuration - also visible in the previous picture. 1617 was built in December 1953 with a steam generator & water tank for passenger service but the steam generator was removed and the water tank converted to additional fuel storage many years ago.



While GP7's and GP9's look almost identical in an exterior view, there were differences in louver placement in the carbody. Matt's picture of Metro North 750 shows a unit that is actually a GP9. Compare louver placement between the 1617 and the 750 and you can see the differences.

HOWEVER, since the last GP7's were built almost 60 years ago and the last GP9's were built some 54 years ago, subsequent rebuildings, modifications, etc have blurred these differences. The most significant difference between the GP7 and the GP9 is internal. The GP7 was built with a 16-567-B engine, which had square airbox covers, while the GP9 was built with the much improved 16-567-C engine, the first EMD diesel motor with ROUND airbox covers. All EMD 2-cycle diesel engines built since the 567-C have had round airbox
covers.

EMD developed a retrofit kit for the 567-B engine that gave that motor some of the advantages of the newer "C" design. Many roads re-fitted (ie "upgraded") their 567-B equipped locomotives. An upgraded block was then known as a 567-BC. In other cases a 567-C engine would replace a "B" engine during a unit rebuilding project. Both blocks are interchangeable in the carbody. I am even aware of some instances where rebuilt 567-B (or 567-BC) engine was put into a unit originally built as a GP9. For example C&NW's ex CGW shop at Oelwein IA did this in the 1970's.

1617 has it's original GP7 carbody (except for the chopped short hood) and it's original 16-567-B motor.

Many used to assume that a geep with dynamic brakes was a GP9. Not a good assumption. Dynamic brakes were an option on the GP7. NP had 20 GP7's; the first 14 were non-dynamic units and the last 6 had dynamic brakes.

Here is a picture of WP 708, a dynamic brake equipped GP7, which currently resides At the Feather River Rail Society museum in Portola CA. Notice the louvers and the dynamic brake blister on the carbody.