WHY THERE WAS NEVER AN SD30

A GP30. Craig Garver collection

    Those of you who know me from other communities online will know I am a staunch advocate against the conceptual SD30. But...why? Following the rest of EMD's catalog, both before and after the 30, EMD catalogued both 4 and 6 axle variants of every model, only deviating in the modern era with the general discontinuation of 4 axle road power in the 90's. So why no SD30? The short answer is that there was never an SD30, mostly due to company priorities at the time. The long answer is a wild tale about what the GP30 was, why it existed, and why there was no market for 6 axles at the time of its introduction.

 

UP 494 is typical of an average GP20. Craig Garver collection

    For starters: we need to discuss the GP20. EMD had been experimenting with turbocharging starting in 1956 with some experiments heralded by UP to produce turbocharged variants of the 16-567. Laboratory testing found 2400 horsepower was possible, however in order to transmit this horsepower to the ground they would need a much stronger traction motor capable of 600 horsepower; their current TM was only capable of about 500. As a stopgap they developed the GP20, which was downrated to only 2000 horsepower. At the same time, they offered the GP18 as a direct replacement for the GP9 in their catalog. Both units were produced starting in 1959. 

CB&Q 504 is a very well restored SD24. Of note is the high nose,
which CB&Q optioned over the low nose.
Ron Zack photo

    The horsepower restriction on the GP20 was unnecessary for 6 axles, as a 2400 horsepower 6 axle would only put 400 horsepower into each motor. EMD immediately offered the SD24 as their premier high horsepower 6 axle locomotive, readily competing with ALCO's RSD15. (They also offered the SD18 as a replacement for the SD9 which carried 1800 horsepower from a roots blown 567.) EMD's catalog in 1959 was as follows:

• GP18 - Roots blown 16-567D1, 1800 HP
• GP20 - Turbocharged 16-567D2, 2000 HP
• SD18 - Roots blown 16-567D1, 1800 HP
• SD24 - Turbocharged 16-567D3, 2400 HP
  

This catalog was almost competitive with ALCO, offering an equivalent to every locomotive in their lineup bar the RS27 (ALCO themselves produced the RS32 to directly compete with the GP20, equipped with a V12-251 making 2000 horsepower). But there was a new contender on the market at the same time, and they brought far more sinister competition than what ALCO was capable of...

    GE exploded out onto the market in 1960 with the U25, a 2500 horsepower 4 axle road switcher locomotive kitted out in GE's newest developments in railroad technology. Equipped with the sturdy GT-598 generator and GE's tried and true 752E traction motor, the U25 immediately lit a fire under EMD to produce something significantly more competitive in horsepower. Of note is that GE (in 1960) had no intention of producing a 6 axle equivalent to the U25, intending to sit on 4 axle power while they developed a 3000 horsepower road locomotive.

UP 634 was once GE 2502, one of a four unit set of production demonstrators turned
U25 demonstrator turned UP unit. Craig Garver collection

    EMD immediately returned to work to produce something to compete with the U25. While EMD was still the dominant force on the market, and ALCO was quickly sliding into obscurity compared to the GM giant, GE was a company large and capable enough to seriously challenge EMD's iron grip on the industry. EMD got to work to upgrade their traction motors and turned to their design department to create an attractive new carbody to replace the GP20's now ten year old hood and cab. EMD quickly introduced a minor upgrade to their traction motor and generator, producing what they dubbed at the time the GP22, with 2250 horsepower.

The GP22 was a stark departure from EMD's previous carbody. Note the large protrusion
which houses the dynamics, main air intake, and headlight.
EMD photo

    The first road capable GP22 was turned out in 1961. While it technically rode on the same frame as the earlier GP20, the carbody was massively redone with a raised engine hood, reoriented radiator, and a much bigger short hood. EMD marketing at the time also requested the renaming of the GP22 to have a higher number in its name than the U25. The expansive electrical cabinet necessitated the raising of a section of the hood, which GM's designers used to create the unique hood shape which defined what was now renamed to the GP30, touting "30 improvements over previous EMD locomotives." A few minor carbody upgrades were also given to the GP30 carbody prior to its introduction as a demonstrator, where it went off to compete with GE's now twelve strong U25 demonstrator fleet.

The same, previously unnumbered GP22, now updated and renamed to GP30. It was introduced
as a demonstrator in 1962, hence its number.
EMD photo

    SD24 production had tapered off significantly after 1960. Very few roads were interested in purchasing large fleets of locomotives in the early 1960's, and fewer were interested in more expensive 6 axle locomotives. The few customers of the SD24 were western roads in need of high tractive effort higher speed power for running freight over large mountain ranges (ATSF, CB&Q and UP) and the massively expanding Southern, in need of more road power for its growing network. By 1961, EMD was still offering the SD24, but nobody was biting. GE did not have any interest in making a 6 axle locomotive, thus EMD focused their efforts on attacking the U25 in its own market. 

Make no mistake, these are not SP units. EMD owned them wholesale, and wanted SP to buy them
and more in repeat orders. They were not successful.
EMD photo

 

    EMD continued to offer the SD24 nevertheless, and targeted SP as a possible customer of new SD24's in 1962 (SP had, conspicuously, been a debut purchaser of the U25). Producing a trio of full SP spec SD24's, paint and all, the three units were sent to SP for demonstrating. The trio ran on SP for several months, gathering data and attempting to sell to SP management. SP mechanical was not impressed with the SD24; while it was more fuel efficient than an SD9, it was only marginally more effective in tractive effort, and paled in comparison to SP's latest experiments in German built diesel hydraulics. SP ultimately turned down the SD24, and the three were sent back to EMD and sold to Union Pacific at a slight discount.

     The GP30 replaced the GP20 in EMD's catalog, and the latter was dismissed. It was always intended as a stopgap, and it had served its purpose by the time the improved GP30 arrived. EMD, however, decided dedicating time to develop a 6 axle GP30 was not worth the effort and money, mainly due to the failure of the SP SD24's and the lack of any major orders. EMD's catalog now lists as follows:

• GP18 - Roots blown 16-567D1, 1800 HP
  
• GP30 - Turbocharged 16-567D3*, 2250 HP
  
• SD18 - Roots blown 16-567D1, 1800 HP
  
• SD24 - Turbocharged 16-567D3, 2400 HP
  

*Although the GP30 carried the same 567 revision as the SD24, it was slightly detuned.

    While the GP30 was attractive from a marketing standpoint, it was inferior to the U25 in performance, which EMD knew and was fully intending to fix. By 1963 EMD was back to the drawing board, developing more upgrades to the generator and traction motors and simplifying the new carbody to compete better with GE. By now, GE's catalog had expanded to encompass the U25B (the former U25) and U25C, a 6 axle version of the U25B made at the request of Oroville Dam. Customers that may have otherwise bought SD24's began purchasing U25C's, such as L&N and CB&Q. By now, the chance to develop a 6 axle GP30 was too little, too late; GE had a 6 axle road locomotive that would effortlessly defeat it in performance. EMD focused their efforts on their new replacement line to reunify their 4 and 6 axle turbocharged offerings.

The last of her kind, the final made of an already rare breed. She sits alone, as it seemed she always
was, high in the mountains of Utah. Down the mountain, in the yards in Salt Lake City, her sisters
once worked for UP; by the time of this picture in 1984, she is truly alone. But here, despite her
uniquity and the rest of the world passing her by, she toils away, doing what she was made to do.
Don Strack photo

    It is here where something very curious happens, and something often cited in discussions of 6 axle GP30's. Kennecott Mining Company, a large mining installation based out of Utah, came to EMD with a request for a locomotive. KMC needed a locomotive to service their Magna smelter, and were not interested in electrics. Magna sits high on the plains of Utah, at 4,000 feet elevation, and KMC was concerned about a roots blown locomotive being too weak in high elevation for their work, and thus requested a 6 axle turbocharged locomotive. EMD responded with an SD24 in 1963, numbered KMC 904. It was truly bone stock, carrying no optional extras other than dynamic brakes. 904 would be the final SD24 built. KMC did not purchase an SD30. They sent a request to EMD, which was filled with an SD24 by EMD themselves.

On display at the 1964 New York World's Fair, EMD 1964, one of the GP35 demonstrators,
rests outside GM's display.
Chuck Zeiler photo

    In 1964, EMD's upgraded carbody improvements were introduced with what was now called the 35 line. EMD matched GE's horsepower threshold with the 2500 horsepower GP35 and now introduced a 2500 horsepower 6 axle dubbed the SD35. Roots blown equivalents were also offered in the GP28 and SD28, but both were mechanically identical to the GP18 and SD18 outside of name and carbody. EMD had finally unified the 4 and 6 axle locomotives under one common carbody and horsepower rating, four years after they first split. The GP30 and SD24 were discontinued in favor of their 35 equivalents. EMD's catalog was then remade as follows:

• GP28 - Roots blown 16-567D1, 1800 HP
• GP35 - Turbocharged 16-567D3A, 2500 HP
• SD28 - Roots blown 16-567D1, 1800 HP
• SD35 - Turbocharged 16-567D3A, 2500 HP 

 　It should be apparent by now that the introduction of the U25 caused a lot of trouble for EMD's catalog. The split between the 4 and 6 axle turbocharged locomotives that occured in 1960 that was not amended until 1964 was largely due to the advent of the U25 and the threat it placed on EMD at the time. Their direct competitor to the U25, the GP30, was a stopgap model made to immediately compete with the U25 instead of be a standardized offering in their catalog. The SD24, which was not outdated electrically and horsepower wise but was not standard physically, went unreplaced in EMD's catalog despite the development of the GP30 largely due to a severe lack of major orders. The SD35 was much more successful than the SD24, producing a respectable 360 total. 4 axles were still outselling 6 axles by a large margin, although the seeds of change were planted, paving the way for the SD40 and SD45.

A C&O SD35. The radical departure from the carbody of the SD24 is partially deceptive;
the two models have the same length frame and were not far from each other in
performance and electrical gear.

    Thus, no SD30. There was no 6 axle market during the lifetime of the GP30 which would warrant having one to begin with. What's more, the SD24 still made competitive horsepower and had yet to leave the catalog, so any prospective 6 axle purchasers could simply buy SD24's. An SD30 would not provide any meaningful upgrades to the 6 axle frame aside from standardizing an already experimental carbody on an outdated frame. This is why EMD opted to revise the frame for the 35 series, bringing the standard SD35 which was largely identical to the GP35. Alas, for GP30 fans, there was no 6 axle version offered, although the reality of EMD's catalog is somehow stranger than fiction.

    (In 2013, EMD produced an upgraded SD40-2 with a new cab and carbody for CP Rail which they named the SD30C-ECO. This model shares nothing with the aforementioned nonexistent SD30 and does, in fact, exist.)

THE TUNNEL MOTOR - and EMD's Extended Fight with Thermodynamics

 

    Southern Pacific had a unique problem in the late 1960s and early 1970s. While most other roads had success operating EMD's latest line of road locomotives (at the time, the 645 line), SP was running into trouble on its mountain routes. EMD's SD45 (of which SP had over 300) were overheating in tunnels and snow sheds at an alarming rate. Even stranger still, GE's new U33C was not having any issues at all with overheating and was operating perfectly fine through the road's many bores and sheds. What was going on here? SP embarked on a quest to find out, and so began the saga of the "tunnel motor", or EMD's never ending quest to meet SP's demanding operating conditions.

    First, an extremely simplified discussion of thermodynamics and how EMD radiators perform compared to GE radiators. Pictured here will be an SD45 and U33C, however the following description applies to almost all of EMD's GP/SD line and GE's Universal line with a few notable exceptions (covered later on in this post). 

    EMD's SD45 draws cool radiator air from around the shuttered intakes at the rear of the unit. When extra cooling is necessary, the radiator automatically regulates itself using the radiator shutters and fans. In the case of the SD45, two banks of three radiator cores with two separate sets of shutters and three distinct fans are present. One fan activates, then one set of shutters, then one fan, then the other shutters, then the third fan, when necessary. When little cooling is necessary, the two rear fans are used as an air intake while the shutters remain closed. At maximum notch, full load, the engine can sustain itself with all three fans running and both shutters open.

    GE's U33C has one central fan and six radiator cores. Air is drawn from vents on the side of the hood, below the radiator, and drawn upward over the cores. Mounted directly at the top of the cabinet, the radiator fan pushes air over the cores upward. Using a fluid valve to regulate water flow, the radiator allows more or less water through depending on necessary cooling. At maximum notch, full load, the engine sustains itself with the fluid valve completely open and the fan at max speed. This eliminates the need for shutters as well as requires only one engine driven fan (compared to EMD's three electric fans.) 

    One last notable bit of engine tech is the exhaust. On both the SD45 and U33C, a single exhaust stack expels engine exhaust directly upwards. On the SD45's 20-645E3, this stack is positioned on the generator end of the engine (closer to the cab), while on the U33C's 7FDL16E the stack is on the auxiliary end (adjacent to the radiator).

Relative heat diagrams for the U33C and SD45 in an enclosed space.
Notice how the U33C's intake is much lower, and gathers cooler air.

 

    The trouble begins under load in tunnels. Operating in open air, both the U33C and SD45 work as intended; both units expel hot air upward and intake cold air from the engine air intakes without issue. However, when inside a tunnel, it was found that SD45s were inhaling hot air as a combination of engine exhaust and hot radiator air due to the close proximity of the radiator intake and fans to the radiator exhaust. This problem was not extended to the Universals, as their lowered cool air intake was able to intake colder, lower air than the hot rising exhaust from the engine and the already spent hot radiator air.

    SP was a firm believer in improving a product as much as possible, and went to EMD with their findings. In response, EMD developed the "Tunnel Cooling Modification" which reoriented the radiator to be more akin to GE's design, placing the cores at the very top of the hood and placing the fans underneath them blowing upward. Depending on installation, a different configuration was used; on the SD45T-2, three fans are present, on the SD40T-2, only two are necessary. On EMD's tunnel cooling modification, in place of the fluid valve regulator present on the Universal, shutters placed above the cores were used, opening as cooling was necessary. 

Builders photo of SSW 9163

Exposed radiator cores behind
open shutters; a solid photo
of how the Tunnel Motor style
radiator was oriented.

    EMD would eventually make changes to their radiators to make them perform better in enclosed spaces. Effective after 1975, baffles between the separate fans and requiring the shutters to open immediately upon fan activation (rather than drawing air through the other fans, which would be significantly hotter than the air around the shutters) were made standard on the Dash 2 line and all future models with the same radiator design, continuing to the present. Tunnel cooling modifications were offered on the 50 Series of the 1980's, however no purchasers optioned it (SP was not interested in the 50 Series and DRGW's one order of SD50's was a duplicate of a Seaboard order).

    The "tunnel motor" radiator seemed to be more than satisfactory to SP, as they purchased 247 SD45T-2's and 239 SD40T-2's from 1972 to 1980, with DRGW also purchasing a handful of SD40T-2's during the mid-1970's (Rio Grande had similar troubles with their EMD products in similar circumstances). Eventually, after merger with DRGW, SP owned all built tunnel motors, operating them with distinction well into the 2000's on UP. Some were exported to South America, others were sold into secondhand service, and a select few were donated to museums (at least one SD45T-2 and two SD40T-2's).

An MP15DC. The radiator intake is clearly
noted at the front face of the hood.
Craig Garver photo

    While SP was dealing with their troubles in tunnels, EMD encountered a similar issue with their smaller power and overheating; however, unlike the road switchers, the switcher and light road switcher units had a completely different radiator design. Originally introduced in the late 1930's on their S and N line switchers, EMD's switcher radiator draws air from the front and exhausts upwards, across the cores.

 

    This presented a similar issue to the road switchers, but in a different context: when two switchers were run front-to-front (usually SW1500's or MP15DC's), the radiators could not draw enough cold air to keep the engine cooled, leading to overheating. This was most exacerbated on roads using them in road service (namely P&LE, among others) where units would overheat each other facing towards themselves. As it turned out, the tunnel cooling modification was called upon here, where a downsized version of what was present on the SD's was used in place of the standard forward facing radiator fan. Found satisfactory, the tunnel cooling style radiator was made standard on the switcher line. The MP15AC was the first switcher to employ this cooling setup in 1975, and all further locomotives of this caliber made by EMD (such as the GP15 and MP15T) would carry the "tunnel cooling" style radiator standard.

An MP15AC. The radiator has been completely
reoriented, however the rest of the unit is
largely the same on the outside.
Craig Garver photo

    GE never changed their radiator setup in any dramatic way, simply iterating upon it and upgrading it with improved components and customer preferred options. Replacing the shaft driven fan with an electrically blown fan, moving the radiator cores upward in the body, and generally simplifying construction were among the many improvements GE made to their radiator design, up until today's Evolution line locomotives. Ironically, despite the roads findings, the Universals were disliked after the mid 70's recession and were operated minimally by an ailing Southern Pacific. While the U33C's of the 1970's were retired early, EMD's SD45T-2's and SD40T-2's had long and legendary service careers on SP, DRGW, and UP, so it's important to remember the key role GE had in the creation of an icon of western railroading in the late 70's and 80's.