The question that I have is this,,,what determines how good a steam locomotive will draft,,,,when working,,,,...
Is it the distance between the blast nozzle,,and the petecole pipe???
or the size of the blast nozzle,,,whether being a muli-port nozzle,,,or singleport nozzle....thanks Pat

My response would be; what is ultimately important in drafting within the smokebox setup is making sure the exhaust is filling the stack as centrally as possible. The exhaust fans out after leaving the exhaust nozzle(s) (Climaxes have two) like a cone. If that cone is too high it won't seal the stack threreby making bad draft. Or, too low which was the case with the climax I worked on, you will again have less than 100% draft available and will start to erode the base of the stack base / ceiling of smokebox. The size of the bridge, or nozzle opening will affect the exhaust back pressure ultimately affecting the power of the locomotive. There are a number of factors that play into setting up the draft in the smokebox for each class of locomotive and class of service. It all has to be right to do a good job.

Pat,

Entire careers have been expended trying to come up with the ultimate answer to that question.

I have some pretty good info on my webpage at:

http://www.trainweb.org/tusp/exhaust.html