Respectfully – In really simple terms can anyone tell me what tunnel motor refers to?
Thanks in advance
RC
The radiator air intakes in this model were located along the deck to allow more fresh, cooler air to enter and less hot exhaust fumes lingering around the tunnels ceiling.
From what I’ve learned, the tunnel motor was designied for the Southern Pacific due to the long tunnels and snow sheds on the route across the Sierra Nevada Mountains.
Tunnel motors (SD 40T-2 and SD45T-2) were made by EMD for Cotton Belt, Southern Pacific, and the Denver & Rio Grande with air intake grills down low near the back of the frame so hot exhaust gasses wouldn’t be sucked back into the air intake and choke down the prime movers in tunnels.
The air intakes are for the radiators, so choking the engine is not part of it.
While cool air is denser than warmer air, you have to take into account all of the mixing of the air due to the exhaust and radiator fans. I have heard that the air down low rapidly becomes hot in a tunnel with a slow moving train going through it. From what I have heard, from multiple sources, is that the radiators were designed to allow the engine to run cooler outside of the tunnels so that it would take longer to overheat inside the tunnels.
Look at the locomotives to the right coming into this picture (it’s not a good one but gets the point across) The first locomotive is an SD 45T-2 See how the intake grills at the bottom of the rear of the locomotive are located almost at the walk way level? That’s a tunnel motor air intake hence the “T” or “Tunnel” intake. The second locomotive comming into the picture is an SD 50. See how the air intakes at the rear of the locomotive are above the walkway and almost even with the top of the locomotive? Hence there is no “T” in the SD 50 due to the location of the intake grill…chuck
