Re: Extended Smokeboxes

Speaking in generalities, smoke boxes were an area of a tremendous lot of experimentation with drafts, back pressure, etc. The goal was usually to try to improve the engine's efficiency with improved drafting and/or reduced cylinder back pressure (with different exhaust nozzle designs) and in the process, better spark emmission control. Sometimes these devices required more room--hence the elongated smoke box. Certainly Union Pacific was very noticeably envolved with this process--look at their extreme elongation on earlier power like Mikes, Pacifics, 2-10-2s, etc.
Les Clark