Aren’t the performance claims for the 5AT a bit exaggerated?

he following answer is taken from Wardale’s response to Leonard Staghurst whose letter was published in Steam Railway #277 (copied below):

“Unfortunately Mr. Staghurst’s comments betray his lack of knowledge, not only of what is possible with steam traction but also of what has already been achieved. Consider the following.

ItemSAR 26 Class 4-8-45AT 4-6-0
Type of LocomotiveRebuild of 1950's designNew design
Quality of Thermodynamic DesignRestricted by structural limitations of existing designState of the art
Number of Cylinders22
Simple or CompoundSimpleSimple
Valves / Valve GearPiston / WalschaertsPiston / Walschaerts
Boiler Pressure (lb/in2)225305
FuelCoalGas oil or deisel
Ash Content of Fuel15%0
Fuel Calorific Value (Btu/lb)12,00018,400
Engine Weight - Excluding Tender (tons)12380
Maximum Indicated h.p.5060 (peak of measured i.h.p. curve)3460 (calculated)
i.h.p / ton of Engine Weight41.143.3

The above figures, which are amply supported by other data, show eloquently enough that the calculated power capacity of the 5AT is perfectly realistic, and I regard achieving it as a formality (and surpassing it a probability) – even on this planet! Likewise all factors concerning thermal efficiency, except the target combustion efficiency at maximum evaporation, which I have acknowledged will be a difficult problem. But that does not mean impossible, simply that very good engineering will be required to achieve it.”