GP-38/GP-39

Ok what is the difference between the two? I know the 39 is turbo charged and the 38 is not and they are close in horse-power.

But why would a railroad pick one over the other? And a lot of railroads had them both. Thanks

As I recall, the GP-38 has a 16 cylinder roots blown 645 rated at 2000hp. The GP-39 has a 12 cylinder turbo charged 645 rated at 2300hp. A lot of railroads preffered the simpler maintenece that came without the turbo on the 38, although a number went for the lighter axle loading of the 39.

GP-38 was MUCH more popular: I assume this means that (at least with low-mileage units for secondary service) the maintenance hassle of a turbocharger was greater than that of an extra four power assemblies.

Turbocharged engine bettter at hich altitudes: supposedly this is why the Santa Fe, with much of its system fairly high up, bought a large fleet of GP-39-2. (Or so it was suggested at the time in the railfan press. Santa Fe seems to have been more turbocharger tolerant than many railroads, rebuilding GP-30 and GP-35 with turbocharged engines rather than de-turboing them.)

Turbocharged engine was more fuel-efficient. In the early 1970s nobody seems to have cared much about this: EMD didn't even bother cataloguing a GP-39-2 when the Dash-2 line was introduced in 1972. After the mid-1970s "energy crisis" people became more conscious of such issues: GP-92-2 started selling then.

Allen Hazen wrote: Turbocharged engine bettter at hich altitudes: supposedly this is why the Santa Fe, with much of its system fairly high up, bought a large fleet of GP-39-2. (Or so it was suggested at the time in the railfan press. Santa Fe seems to have been more turbocharger tolerant than many railroads, rebuilding GP-30 and GP-35 with turbocharged engines rather than de-turboing them.).

Thats interesting Allen as the Santa Fe was not high on the GP-40, But they like the SD-40.

The problems with the turbo come about in switching/local service. A 2 stroke needs constant pressure charging. On the turbo EMD models, this can't be accomplished at low speeds. The turbo doesn't provide enough pressure. This is overcome by having a clutch. It is engaged at low speeds, then the turbo freewheels at high speed. Constant clutching/de-clutching wears this out. This is why some railroad have taken turbos off of 40 series, when demoted to local/yard. This makes them a 38.
Where I work, there used to be a large fleet of the GP39-2. This is because we have a heavy, low speed line. The 39 is more efficient, but the hp of the 40 was not needed., just the t/e.
On a similar point, EMD made the GP15 with both a 8 cylindar turbo, and the 12 roots blown. Didn't Seaboard or early CSX get some switcher with the 8-645T?

Another difference between the two is, the GP39 and the GP39-2 used .86 Grids for Dynamic Braking and the GP38 and the GP38-2 used .66 ohm Grids for Dynamic Braking. They both used the same amount of Traction Motor Field Amps, but the Dynamic Braking produced more feedback voltage on the GP39 and the 39-2

Engineer Spike wrote:On a similar point, EMD made the GP15 with both a 8 cylindar turbo, and the 12 roots blown. Didn't Seaboard or early CSX get some switcher with the 8-645T?

Yes, that unit is called the MP15T, and CSX still has most (all?) of them in service.

The GP15 with the Roots blower 12 was the GP15-1; the GP15 with the turbo 8 was the GP15T. CSX still has most (all?) of their GP15Ts, too.

WVU wrote:Another difference between the two is, the GP39 and the GP39-2 used .86 Grids for Dynamic Braking and the GP38 and the GP38-2 used .66 ohm Grids for Dynamic Braking. They both used the same amount of Traction Motor Field Amps, but the Dynamic Braking produced more feedback voltage on the GP39 and the 39-2

The GP38-2 was available with either the 0.86 Ohm or the 0.66 Ohm grids.

The 0.86 Ohm grids essentially operated the same as their 0.66 Ohm counterparts. The difference being that the maximum braking effort (and subsequent grid shorting - as used in the optional extended range dynamic braking package) would occur at different track speeds.

JR

JR by no means am I questioning what you are saying about the GP38-2 and having .86 ohm grids, but in my 30 years on the railroad, I have never seen a 38-2 with .86 ohm grids. I have calibrated many 38-2 units with regular Dynamic Brakes and Extended Range Dynamic Braking and I have been setting the electrical limits on them for years. JR thanks for letting me know about the 38-2 units with .86 ohm Grids in them. I guess EMD would build them for however the rail company preferred.