The 65 later engines were also fitted with a vertical hinge between the driving units so positioned as to even the weight distribution between the front and rear driver sets. These engines could run at 70 mph pulling a 20-car passenger train.
6 more locomotives of identical design were leased as #3800-3805 for the Denver and Rio Grande Western in 1943, which returned them in 1946. At this point they went to the Clinchfield as E-3 (670-675) and retired in 1953.
When the UP resumed building 4-6-6-4s in 1944, they took the opportunity to substantially rework the boiler of the 1930s variant. The tubes were shortened by 2 feet, 94 sq ft of circulators were added to the firebox heating surface, the grate area jumped by 24 sq ft, superheater area increased by 91 sq ft, boiler pressure rose by 25 psi, cylinder diameter shrank by an inch ....about all that didn't change was the driver diameter.
Union Pacific's general mechanical engineer Arthur H. Fetters suggested basing a simple articulated design on the 4-12-2, thus invented the Challenger wheel arrangement. UP eventually bought 105 4-6-6-4 locomotives for express passenger and freight service. The first group of 40 were first numbered 3900-3939, but later renumbered 3800-3839.
According to the locomotive diagram, the first 10 had Worthington feedwater heaters, then next 5 had Sellers had exhaust steam injectors, and the last 25 Worthingtons. This latter group arrived in 1937. They also put 5 more tons of adhesion weight, bulking up to 407,340 lb and increasing overall engine weight to 584,950 lb.
| Specifications | |||
|---|---|---|---|
| Class | 4664-2/-3 | 4664-5 | CSA-1/CSA-2 |
| Locobase ID | 341 | 6613 | 1406 |
| Railroad | Union Pacific (UP) | Union Pacific (UP) | Union Pacific (UP) |
| Whyte | 4-6-6-4 | 4-6-6-4 | 4-6-6-4 |
| Road Numbers | 3950-3999 | 3930-3949 | 3900-3939 / 3800-3839 |
| Gauge | Std | Std | Std |
| Builder | Alco | Alco | Alco |
| Year | 1942 | 1944 | 1936 |
| Valve Gear | Walschaert | Walschaert | Walschaert |
| Locomotive Length and Weight | |||
| Driver Wheelbase | 12.17' | 12.17' | 12.17' |
| Engine Wheelbase | 60.37' | 35.08' | 35.08' |
| Ratio of driving wheelbase to overall engine wheebase | 0.20 | 0.35 | 0.35 |
| Overall Wheelbase (engine & tender) | 106.67' | 106.67' | 97.87' |
| Axle Loading (Maximum Weight per Axle) | |||
| Weight on Drivers | 403700 lbs | 404200 lbs | 399840 lbs |
| Engine Weight | 627000 lbs | 634500 lbs | 566950 lbs |
| Tender Light Weight | 436500 lbs | 434500 lbs | 322600 lbs |
| Total Engine and Tender Weight | 1063500 lbs | 1069000 lbs | 889550 lbs |
| Tender Water Capacity | 25000 gals | 25000 gals | 18106 gals |
| Tender Fuel Capacity (oil/coal) | 28 tons | 28 tons | 6000 gals |
| Minimum weight per yard of rail on which locomotive could run | 112.14 lb rail | 112.28 lb rail | 111.07 lb rail |
| Geometry Relating to Tractive Effort | |||
| Driver Diameter | 69" | 69" | 69" |
| Boiler Pressure | 280 psi | 280 psi | 255 psi |
| Cylinders (dia x stroke) | 21" x 32" (4) | 21" x 32" (4) | 22" x 32" (4) |
| Tractive Effort | 97352 lbs | 97352 lbs | 97305 lbs |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | 4.15 | 4.15 | 4.11 |
| Heating Ability | |||
| Firebox Area | 602 sq. ft | 604 sq. ft | 548 sq. ft |
| Grate Area | 132 sq. ft | 132 sq. ft | 108.25 sq. ft |
| Evaporative Heating Surface | 4817 | 4642 | 5304 |
| Superheating Surface | 2355 | 1741 | 1650 |
| Combined Heating Surface | 7172 | 6383 | 6954 |
| Evaporative Heating Surface/Cylinder Volume | 187.75 | 180.93 | 188.37 |
| Computations Relating to Power Output (More Information) | |||
| Robert LeMassena's Power Computation | 36960 | 36960 | 27603.75 |
| Same as above plus superheater percentage | 49096.20 | 47041.05 | 34153.39 |
| Same as above but substitute firebox area for grate area | 223908.41 | 215248.45 | 172896.60 |
| Power L1 | 36424.07 | 29281.58 | 23842.85 |
| Power MT | 1193.48 | 958.26 | 788.78 |
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