While we are on the subject of the various favorites in the steam locomotive "Miss USA" contest, can one of the expert "P.E." guys or other authorities explain to me the pros and cons of extending smokeboxes? I understand that it must affect the drafting of the locomotive, but specifically what does it do to it and how? Are there formulas to how much to extend? Why were some engines extended, only to be chopped back in later years? #375 is prime example of this, born an ugly duckling and later chopped to a more svelte appearance. What were the tradeoffs?