Here in the UK, steam-locomotive literature is filled with discussion about steam-circuit improvements in the later generation of steam locomotives. I see that in the US also, a great deal of effort was spent in getting vast quantities of steam efficiently from boiler through cylinders and out the stack. Think multiple-jet blastpipes on the UP FEF-3, or the carefully designed piston valves on the NYC Niagara's. But what about the Frisco's modern power such as the 4300s Mountains? Those stacks look too big in diameter for conventional single-jet blastpipes. Does anyone know if they had multiple-jet blastpipes? And what about valve timings lap and lead? Were they set for uphill slogging or speed? Were the exhaust-side of the piston valves chamfered a la NYC Niagara's to ease the blast? Regards from a UK Frisco fan with a deep fascination for all things steam! Dave
Dave, I have never seen any data or pictures of a 4300s front-end arrangements. Frisco Power and Steam Locomotives of the Frisco Line both mention enlarged dry pipes and branch pipes. It would seem reasonable that given the desire to rebuild the drag-era engines into fast freight locomotives that the process would have included a state of the art blast pipe. Other changes were certainly made to increase speed. The Scullin Disc drivers being the most obvious. With tales of the 4300 and 4400 series able to literally haul the freight at 70 mph, they must have had a modern steam locomotive-wise front end. That front end could keep back pressure low at top speed, while inducing the needed draft to generate steam to feed a pair of 27" on 4300 or 29" on the 4400 cylinders. Hopefully, someone can provide hard data on the 4300/4400 drafting arrangement. I am looking forward to it!
