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California's Railroad to the U.S. 1861 - 1996

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Model Train Help EBook

Southern Pacific GP38-2

4-stack EMD GP38-2 locomotives

SP 4800 - 4844


4-stack GP38-2 from Tom Fassett, and from the photos contributed; the only unit to be Speed Lettered.


A number of SP's GP38-2's were converted from two to four exhaust stacks, these include, but are perhaps not limited to:

Photo collection of GP38-2 detail images


I guess like most people, (surely I can't be the only one on the world), I 'assumed' the dynamic brake grid extended the entire width of the hood, which meant (to me), that the exhaust delivery pipes went through the grids. As it turns out this is not the case, the grids are only housed in the sides of the hood. Things become much more clearer when you have the facts at hand. I hope you find this as fascinating, as well as, as useful, as I do... RAP


This text and graphics is © midAmerica Correspondent - reproduction without permission is denied...

I saw SP 4825 parked at a good location and got a view inside the engine bay.

Basically, the exhaust pipes from the cylinders exit vertically into horizontal collectors. The front four cylinders join in a horizontal "can" and look like the legs of an animal holding up the body. The collected exhaust exits the "can" at the top of one end (looking like the animal's neck extended upright) and vertically passes through the hood top. The two front "cans" have the exhaust outlets at their forward ends, the two rear "cans" have the exhaust outlets at the rear ends.

The forward and aft exhausts go directly through the hood top. The inboard exhausts go through the flat bottom of the dynamic fan enclosure/box through rough flame-cut holes that fairly closely fit the exhaust pipe shape. The air gap is about 1/2 inch all the way around the exhausts.

A close look at the dynamic equipment indicates that the electric heat exchanger "radiators" are only in the spaces immediately behind, and parallel to, the large air inlet grates visible on the sides of the hood. From inside the hood, there is a sheet metal duct/box that encloses the area from the air inlets to the left and right sides of the dynamic fan enclosure/box. The grids do not appear to get any closer to the fan blades than the apparent diameter of the fan. The front-to-aft size of the fan enclosure is just slightly larger than the diameter of the fan. The fan enclosure/box depth is about 10 - 12 inches from bottom to hood top. The bottom of the fan box also has a central opening to extract hot air from the engine bay.

So, the exhausts don't actually mix with the dynamic grids. They just reduce the effective fan draft by the amount of leakage around their passageways through the fan enclosure. Considering the large size of the existing engine bay air opening to the fan enclosure, I don't think they have any noticable effect.

The choice to use the "four exhaust" system probably allows the use of a single "four-cylinder" pattern of exhaust collector and stack (they all looked approximately the same). That should be less expensive to stock and replace.


I made one more trip to see the GP38-2s to compare the two-exhaust version with the four-exhaust version. The "two" version was SP 4838, still in the original delivery paint. It also appears to be "as-delivered" under the hood.

As I speculated, the two-exhaust design uses large exhaust collecters that are a much more costly design than seen on 4825. The outboard units collect six cylinders directly and share a connection to a single central section that collects the four cylinders that are directly under the center of the fan plenum.

I have added color to the section that has the grids, so as to make it clearer.


SP GP38-2 page


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the text and graphics is © midAmerica Correspondent - reproduction without permission is denied
All Corrections, Additions and Flames should be aimed at Richard Percy espee@railfan.net

Sunday, June 17, 2001 6:11:14 AM