NYC A couple of Pacifics

Two Pacifics very different in appearance. The spiffy 6408 was built by Brooks somewhere between 1905 and 1915. 4915 was built by Schenectady in 1926, seen with her train somewhere on the Michigan Central or CCC&StL. Both from my Harold K. Vollrath collection.

 

Interesting comparison of two locomotives erected about 15 years apart, and only a few miles apart. The Brooks Pacific appears to have continued leftover 19th century design and technology. Whereas the ALCO Pacific is a far more modern design. I'm with Ken, I'd like to see a performance comparison.

 

Also, the photo of the 6408 is obviously a builder's photo so it looks brand new and is a true beauty. It would be neat to see the builder's photo of the 4915 too, if one exists.

Generally though, the 6408 still looks more genteel from earlier days and the 4915 looks more industrial entering the modern era of railroading.

Great photos.

Doug

 

Let's ask someone who was there.

Of course, he's talking in general terms, and here is talking about the USRA designs. But the state of the art was the state of the art. The USRA light Pacific didn't differ that much from the 6408, or Santa Fe Pacifics numbered in the 1200, 1300 and 3500 series, or any number of other theoretically more custom designs. And the 4915, or the Pennsy K-5, the Santa Fe 3400 Class, and many others were only modest improvements on the USRA heavy Pacific--at least until they got rebuilt, like 4915 in the photo, with box section drivers, feedwater heaters, and a host of other improvements that helped them avoid shaking themselves to pieces and helped them make more steam.

In other words, they perform about the same when hauling the trains they were designed to haul. Hook the heavy Pacific up to the lighter train normally hauled by the light Pacific, and it becomes quicker and faster, as it is no longer straining to make enough steam to sustain that speed. It isn't balanced to be sublimely happy at that speed, but it gets the job done. It could probably haul a light train almost as well as a Milwaukee Road 4-4-2, especially after getting box-pok drivers. It might have a little more problem with vibration and stability, in exchange for being able to haul a heavier train at slower speeds in a pinch. In short, either engine could produce excellent performance if its load were light enough. But it wouldn't be using the whole of its cylinder size with a light load, and it wouldn't be at its most efficient. It would start the train easily, but at high speed would be straining, and slowly shaking itself apart.

As shown, with the light Pacific as built and the heavy heavily rebuilt, they're almost apples and oranges. But the comparison is interesting, because as rebuilt as shown, the 4915 is now intended to haul at streamliner speeds about the same weight train that the 6408 was intended to handle at 55. That isn't what the 4915 was originally built for, but that's what it was rebuilt for.

That's a different type of rebuild than the 4915, but the effect is not dissimilar. The result is an engine better able to move a lighter train at streamliner speeds. Rebuilding heavy Pacifics was a fairly easy way to get Hudson-like performance for light trains. The Frisco seems to have rebuilt light Pacifics into these light Hudsons because they were too fond of Mountain types at an earlier date, and never got around to buying a lot of heavy Pacifics.

These quotes are from High Iron, written in 1938.

 

The 6408 was built 12/05 scrapped 6/24. 75" drivers 200 BP 28520 TE .The 4915,4917 were brought from the MC to the B4 12/27 . These were the locos
used on the J W Riley . Blt. 11/26 RT 5/52 , SS 54 . The 17 blt. 11/26 RT 5/53 , SS 7/53 . The 4900s were K-5 b 79" drivers 210 bp , 47350 with booster .
As with any loco with the increase in driver size and larger cylinders you had to have an increase in the amount of steam that could be produced for the increased power and the staying power or steam production of the boiler . As with the J-1 Wheel size and cylinders were the same but the TE was up to 53200
so the firebox size was increased and the boiler cap. increased and pressure to 225 bp . These locos were able to run 100 mph + with a heavier train than the 6408 . LEW

 

I got a little lost in there. The J-1 had the same cylinders as which?

I would like to see a comparison between the Frisco Hudsons and heavier Pacifics as modernized. You only need a larger cylinder to move a larger train. To haul a given train faster, you don't need more cylinder, you just need more steam. There is no gearing; the size of the driving wheels is what determines the final drive ratio. If you have more steam, you can keep supplying the cylinders even when the drivers are making more revolutions per minute, and the valve is opening to admit steam more often.

I'm uncertain how much difference a smaller cylinder would make. It seems to me a smaller cylinder would be more efficient, if the locomotive's job involves hauling a train of modest weight at streamliner speeds. But I never heard of a railroad rebuilding their Pacifics with smaller cylinders during the passenger train speedup of the 'thirties. Did it just not make enough difference? Was the extra efficiency of smaller cylinders not worth the expense? Did they not do it because it would make the Pacific less able to pinch hit on slower, heavier trains (putting a lot of money into making a locomotive less flexible and all-around capable might not be a healthy career move for a master mechanic)? Or am I all wet about smaller cylinders being more efficient?

 

The K-5 4-6-2 had the same size cylinders as the J-1 4-6-4 . The tractive effort on the K-5 was around 38000 . On the J-1 TE was 42000 . BP on the
K-5 was 205 lb. and 225 lb. on the J-1 . The 20 lb. greater steam pressure was probably the reason for the higher TE in this case . These engines I think
are a perfect example of what you say about cylinders. Higher steam pressure , larger firebox , and a bigger boiler for more steam . The next step up would be a
4-8-4 with out increasing the cylinder size. LEW