• GP38/-2 vs GP39/-2

  • Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.
Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.

Moderator: GOLDEN-ARM

  by USRailFan
The GP38/GP39 and their Dash 2 counterparts were very similar in performance (GP39/-2 have 300 more horsepower, and turbo, but four less cylinders).

What were the advantages/disadvantages of one type over the other, since both sold fairly well (BN even buying large numbers of both)? At first glance one would not think there would be a market for two so similar locos from the same manufacturer?
  by joydivision350125
GP39 -- better fuel consumption numbers. Four fewer power assemblies to maintain.

GP38 -- no turbocharger to maintain, a huge expense. GP38s also make more sense for lower-speed operations, since the turbo gives few, if any, benefits below 30 mph.

  by Typewriters
As with most topics regarding locomotive design and locomotive marketing, it's not that simple. I'll try to be brief.

The market for such locomotives was initially plumbed by ALCO in 1963 with its C-420. This was a 2000 HP turbocharged locomotive with all the most modern features. It began to sell rather decently.

Electro-Motive responded in its new "1966 line" with the GP-38. This had a normally aspirated engine, and direct-current transmission. While the major focus of the line was the new, high-horsepower turbocharged and alternator-rectifier locomotives the GP-38 did begin to sell too.

General Electric finally responded to this market in 1968 with the beginning of production of its U23 line. These units were turbocharged, and rated 2250 HP for traction. It seems that GE decided to up the ante in terms of horsepower in order to make itself a niche in this market.

At this point, it's obvious that in one sense ALCO and GE had an advantage over the EMD unit in terms of ability to produce rated horsepower at any altitude (few rail lines are at exactly sea level.) All manufacturers of turbocharged locomotive engines have made this advantage apparent, time and again, over many years. Moreover, GE had a horsepower advantage over both the ALCO and EMD units.

At about the same time as the U23 was introduced, then, the 39 series appeared. This was a turbocharged locomotive with AC-DC transmission standard (AC-DC was optional on the U23, and later on the normally aspirated GP38 as well.) Electro-Motive now had the advantage of being able to offer a range of units, essentially, in terms of price and performance. Consider three basic configurations:

GP-38 normally aspirated, direct current
GP-38AC normally aspirated, alternator-rectifier
GP-39 turbocharged, alternator-rectifier

This gave EMD the ability to essentially be able to bid on any specification required by any railroad for units in this general range of performance. Were EMD to bid against the C-420 with the GP-38 it could point to lower maintenance costs. If compared to the U23 it could point to higher output ..and of course in any case, parts commonality with other EMD units sure to be finding their way onto the roads at that time (40 and 45 series units.)

Operationally it was easily possible to match the GP-38 with the SD-40 with almost identical minimum continuous speeds, and ordered properly, similar weight per axle. The GP-39 did have slightly higher power and Performance Control, but the important point was full output at any altitude and one might expect operation with other turbocharged units in these conditions; if that were true, then, the GP-30, GP-35, GP-40 and SD-45 all also had performance control which in all cases but the 30 lost much more than 300 HP at drag performance speeds (1000 HP in the case of the GP-40, as an example.)

Hopefully this is a little easier to understand than just the most basic comparison of number of cylinders and turbocharger or no.

-Will Davis

  by Allen Hazen
As usual, Will Davis has nicely summarized the issue. (He has his own website with a -- not too densely populated -- forum for serious students of locomotive history.)
Minor edit: The GP-39 was also available with straight DC transmission. EMD standardized on AC/DC for its Dash-2 line (introduced 1972), so GP38-2 and GP39-2 are all AC/DC... as are GE's B23-7 (introduced 1977).
  by Engineer Spike
I question the high altitude abilities of the 38. True the free turning turbocharger might be better, but even the 38 intake air is pressure charged, via the roots blowers. On the other hand, in switching service, the clutches on the turbos wear out.

One of the other engineers whom I worked with came from the mechanical department. We had many mid HP units, GP38, GP39, U23B, and C420. The 39 out numbered the 38 by a wide margin. My friend said that the CMO liked 12 cylinder because of less crank flex.

The 39 seems to be a real specialty unit. Why did BN buy so many, not for local service, but for short fast piggy back trains? Did they feel that the cost in fuel and repair, was worth loosing 700 hp, in not buying GP40s?
  by Allen Hazen
Engineer Spike--
Not sure about this, but I don't think BN was a big purchaser of "genuine" GP-39: they used the designation "GP-39" (often with a suffix marking the rebuilder: "E" for those done by Electromotive, don't remember the rest) for heavily rebuilt GP-30 and GP-35 units, which were typically rated at around 2300 hp.
The Santa Fe, on the other hand, WAS a big buyer of GP39-2: at the time speculation (in "Trains," I think) was that this motivated by altitude performance... leading to editorial surprise when the Reading ordered the type.
  by Allen Hazen
A bit of checking, on the web and in my library…
BN ***did*** buy forty real GP39-2. Not sure this means they actually preferred the 2300 hp units for mainline service: they also acquired twenty-five GP40-2 and fifty GP50.
Note that these BN purchases were a minority of the GP39-2 on BNSF predecessor railroads: ATSF had 106 of them.

In contrast, BN had 180 GP30/GP35 rebuilds which they CALLED GP39E, GP39V, and GP39M, depending on whether the work was done by EMD, VMV, or MK. In their technical specs, they had remarkably little similarity to real GP39. They had turbocharged 16-cylinder "645D" engines (meaning 645 power assemblies on D-block: GP30 and GP35 had 567D engines, so these could have been the original engine blocks, though of course there is no guarantee that the engine block on a locomotive when it left the rebuilder's shop was the one it had when it entered the shop). Most of these locomotives were rated at 2300 hp (though apparently at least a few were rated at the 3000 hp you would expect from a turbocharged 16-645). Why the lower rating? I don't know. The suspicion that the old blocks weren't robust enough for full 16-645 power occurred to me as a possibility, but another is that something like the original cooling system was kept (the units tend to LOOK like GP30 or GP35, and don't have the three 48inch radiator fans of a GP40), and this wouldn't handle the extra power and heat.

"Intermediate power" locomotives are good for local freights and heavy switching: services that are relevant to carload freight. With the retreat of Class 1 railroads to unit train and intermodal service (I know carload freight isn't completely dead, but you know what I mean!), I suspect that BN's management after the completion of their "pseudo-GP39" rebuild program may have found itself with more intermediate power than it needed. At which point bunches of 2300 hp units might have found themselves on trains for which a smaller number of more powerful units would have been first choice…

(But remember my amateur status: this is my interpretation of what has been reported in the rail fan press.)
  by Engineer Spike
I knew about the real GP39-2 on BN because I was an engineer there. The first ones were often used on the short piggyback trains, which was used in certain corridors, like Chicago-Twin Cities.These trains were to compete with regional truck routes.

BN did have lots of medium sized power. The GP39E, M, and V were a good locomotive. At the time, there were still lots of geeps still in local service. Many were pretty ratty. That program was at nearly the same time as the GP28 program. This was a 1800 hp unit, built on Geep frames, with a GP38 style car body. Once I did have a unit grain train with some of the fake 39s, and GP38s. At that time they were power short, and leasing lots of junk.

My question is still if the GP38 was really bad at high altitude. They are still force aspirated by the roots blowers, or is it rail fan rumor. Remember that many of Santa Fe's came in the late 1970s, when the supply of oil was thought to run out any day, and the supposed OPEC oil embargo was going on. Although the 39 is more complex, with its turbo, maybe management was willing to sacrifice it for less fuel usage.
  by timz
Load-test section of the GP38-2 service manual says it's supposed to put out 90% power at 5800 ft altitude-- at 60 deg F I guess.
  by Allen Hazen
re: Timz (one post up)
5800 feet seems high enough to cover much of the Santa Fe's opertions, though not all. (I think I remember that the pass (Glorieta?) on the main line east of Albuquerque is over 7000 feet.) And power output would be less on a hot summer day, wouldn't it? So I think that Santa Fe MIGHT have thought the power-loss at altitude onnon-turbocharged 645 engines was enough to worry about. Whether they were right in so thinking is another question, turbo maintenance having been a big issue in the 1970s.
  by Engineer Spike
Santa Fe likely wasn't afraid of turbos. They had been buying them from the start with the GP20, and SD24. The other brands were most all turbocharged, and they had lots of Alcos.