Why do they call it a GS-4?

GS= Golden State class. The 4 refers to the 4th design in the GS series.

On the Southern Pacific GS stood for General Service used in Passenger and Freight work,4 stood for Fourth version

Mikey

On the Pennsy class GS-4 was General Electric Switcher approx 400 HP or in other words - GE 44 tonner.

The SP first called it Golden State and when they wanted more during World War II they changed it to General Service to get it by the War Production Board who didn't permit passenger engine construction.

Sorry, on the Southern Pacific the GS really did mean "GOLDEN STATE", and that "name" carried through the GS-5 class locomotives. However, during World War II, the SP need additional passenger service steam locomotives, but the War Production Board said, "No more passenger locomotives!". The SP tried to tell the WPB that the "GS" class stood for "General Service", however the WPB responded that General Service locomotives had drive wheels no bigger than 75" diameter, where as the SP GS class locomotives like the latest GS-4 & GS-5 locomotives all had 80" drivers, obviously making them 'Passenger service locomotives" and NOT General Service!

 

Thus, the SP GS-6 class 4-8-4 locomotives did NOT have 80" diameter drivers, but 74" drivers for use in freight OR passenger service.

Get's complicated doesn't it?    Those WPB guys were no dummies.

.....

Dennis

To even complicate matters further. The ex Cotton Belt L1 Northerns were classified GS7 and GS8 when they were leased by the SP.The SP leased seven early L1's [GS-7's] (#801, 802, 804, 805, 807, 808, 809), three late L1's [GS-8's] (#815, 817, 818), while T&NO leased three late L1's [GS-8's] (#812, 813, 819).

Another reason to make the Cotton Belt L1 in O scale!

So then the essential difference between freight and passenger engines (steam) is the size of the drive wheels?

this general distinction comes right out of physics.  torque (rotating force) = force x distance (of the applied force to the work).  so for the same torque output (directly related to horsepower through RPM), a smaller "distance" (wheel diameter) will yield a greater force.

There are other issues concerning passenger/freight steamers - such as steam line 

connections for heating passenger cars, but the driver size is a good but -very-

generalized place to start. Most passenger locos 2-axle leading trucks also, as they

guide the loco better at high speeds. This was not universal with high-speed steam, though (NKP Berkshires; high-speed freight.) 

 

One of the most famous passenger steamers were the N&W J-class 4-8-4's - and their

drivers were only 70" in diameter - down in freight loco territory.

But, the N&W locos ran through very hilly country and big 79" - 80" drivers might

have had the loco down on its knees going upgrade (kinda like PW O-gauge...). Also

wasteful of coal.

 

Example: the NYC J1 and J3 classes of Hudsons had 79" drivers for use on the "Water

Level Route" (the NYC had few grades over most of its system) - but the B&A subsidiary version of this same loco - the J2 - had 75"/76" (I forget which) drivers as they had

to handle the Berkshire Mountains in W. Mass. So they need more tractive effort (TE).

Also be aware that "letter and number" classes change with every railroad. A "G" loco class for one railroad would be a totally different loco for another RR. The RR's picked their own numbers for their own classes with no regard whatsoever to what another railroad was doing.

 

For example, a N&W "J" is a 4-8-4, but on the NYC, a "J" is a 4-6-4 Hudson, and on another railroad, a "J" class might be a totally different wheel arrangement, or even a diesel.