You may notice four exhaust stacks on the roof On the original EMD design there were connectors between sections of exhaust manifold, and these are subject to FRA inspection for leaks. A V16 engine has four sections to the manifold, with four "legs" on each section connecting to four cylinders. The connectors in question are between sections of manifold, so that there are only two exhaust stacks on the roof. By doing away with the connectors (and their inspection), each section of manifold then has its own exhaust stack. Thus the four stacks. You may ask why EMD did not design it that way from the start, and the answer is that the space occupied by the two center exhaust stacks was also occupied by the dynamic brake option, if the locomotive was so equipped.