Re: Boiler replacement on C's

I believe the key word here is drafting. Nobody extended smokeboxes like the Union Pacific. Good comparisons can be made against S.P. locomotives that otherwise were very similar. Keep in mind that the SP burned oil and the UP burned high grade black dirt. When burning the latter, there needed to be plenty of smokebox room for the mess that came through the flues and tried to go up the stack. Wheelbarrow loads of cinders and junk were shoveled out of the smokeboxes during regular inspections. Also, I think UP probably experimented with drafting more than any other railroad--witness their Sweeney stacks.
:es Clark