▁ 4 0 ▁degrees ▁apart . ▁For ▁the ▁ 1 8 ▁cyl inder ▁design , ▁it ▁was ▁possible ▁for ▁firing ▁events ▁to ▁be ▁inter la ced ▁over ▁all ▁six ▁banks . ▁This ▁led ▁to ▁the ▁even , ▁bu zz ing ▁exhaust ▁note ▁of ▁the ▁D elt ic , ▁with ▁a ▁charge ▁ign ition ▁every ▁ 2 0 ▁degrees ▁of ▁c rank sh aft ▁revolution , ▁and ▁a ▁lack ▁of ▁t ors ional ▁v ibration , ▁ideal ▁for ▁use ▁in ▁mine - h un ting ▁vessels . ▁The ▁nine ▁cyl inder ▁design , ▁having ▁three ▁banks ▁of ▁cyl ind ers , ▁has ▁its ▁c rank sh aft s ▁rot ating ▁in ▁the ▁opposite ▁direction . ▁The ▁exhaust ▁lead ▁of ▁ 2 0 ▁degrees ▁is ▁added ▁to ▁the ▁ 6 0 ▁degrees ▁between ▁banks ▁giving ▁firing ▁events ▁for ▁adjacent ▁cyl ind ers ▁in ▁the ▁same ▁bank ▁ 8 0 ▁degrees ▁apart . ▁By ▁inter la cing ▁firing ▁events ▁over ▁all ▁three ▁banks ▁of ▁cyl ind ers , ▁this ▁still ▁leads ▁to ▁an ▁even ▁bu zz ing ▁exhaust ▁note , ▁charge ▁ign ition ▁occurr ing ▁every ▁ 4 0 ▁degrees ▁of ▁c rank sh aft ▁revolution ▁with ▁consequ ent ▁reduction ▁of ▁t ors ional ▁v ibration . ▁ ▁Although ▁the ▁engine ▁was ▁cyl inder - port ed ▁and ▁required ▁no ▁po ppet ▁val ves , ▁each ▁bank ▁had ▁a ▁cam sh aft , ▁driven ▁at ▁c rank sh aft ▁speed . ▁This ▁was ▁used ▁sole ly ▁to ▁drive ▁the ▁fuel ▁injection ▁p umps , ▁each ▁cyl