Am I correct in thinking the gp 38-2 was not turbo charged and the 39-2 and 40-2 was?
Yes, you are.
But it WAS, incidentally, supercharged.
Ed
The GP38-2 is Supercharged(a pair of Roots blowers. IIRC). The diesel power plant needs to have lots of air(oxygen) forced into the cylinders with the fuel. The Blower/supercharger is mechanically driven off of the main drive shaft. This is why you see two small exhaust stacks, rather than the large ‘turbo’ exhaust stack further forward on the roof.
Jim
The EMD engine is a 2-stroke engine, as opposed to a 4-stroke. While a 4-stroke has an intake stroke, the 2-stroke does not. So the charge (air plus fuel) must be forced in. In motorcycles, that’s done by using crankcase pressure. In the EMD engine, they don’t do that, so the the charge MUST be pressurized and pumped into the cylinder. Early EMD engines used a supercharger. The first EMD model to use a turbocharger in this process was the GP20. There was also a GP18 that was only supercharged. Note that “8” in the number–a signifier of non-turbocharging. But, bear in mind, the EMD engine MUST be supercharged–turbocharging is an option.
Another fun fact about EMD engines is that they’re not cast but built up out of welded steel plate.
And the classic bore and stroke was 9" x 12". Edit: OOPS, Wikipedia goes with 9 (1/16)" x 10"–wonder where the 12" came from.
Ed
Good Point Ed,
EMD’s turbocharger is sort of unique in the railroad field. It is shaft connected via a centrifugal clutch at lower speeds - at higher speeds, the clutch releases and it is exhaust driven like a normal turbocharger. The advantage of this scheme is that there is less un-burned fuel as the throttle is increased. A normal ‘turbo’ has to spool up as the exhaust gases increase. This give EMD locomotives their fast loading. An Alco or GE would exhaust lots of black smoke(un-burned fuel) until the turbo was up to speed so it could ram enough air into the cylinders. GE addressed this by using microprocessor controls to limit the fuel injection until there was enough ‘boost’ pressure from the turbo unit. This is why GE’s typically have slower loading. This also help address EPA exhaust emissions issues. IIRC, this change started in late ‘Dash 7’ production.
Jim
From the below picture, it looks to me that the F-M opposed engine was probably also a two-stroke, what with the ports and the lack of valves and all:
Ed
You are correct. The F-M OP engine is of a two stroke design. The scavenging blower is just not shown. The scavenging air entered the upper ports after the lower ports were uncovered to exhaust the spent gases. The fresh charge of pressurized air helped rid the cylinders of exhaust gases for the next power stroke.
The first EMD model to use a turbocharger was a UP GP9 in the Fall of 1955. Union Pacific continued experimenting with turbocharging its GP9s. The first EMD locomotive built with an EMD turbocharger was the demonstrator SD24 #5579 in July 1958. Production of the SD24 model started in the Spring of 1959. Nine UP GP9s and GP9Bs were rebuilt with EMD turbochargers in the Spring of 1959. The EMD GP20 was the fifth EMD model built with an EMD turbocharger after the rebuilt UP GP9s, GP9Bs, and production SD24s and SD24Bs.
Ed in Kentucky