▁port ▁lead ▁and ▁in let ▁port ▁lag . ▁These ▁engines ▁are ▁called ▁" un if low " ▁designs , ▁because ▁the ▁flow ▁of ▁gas ▁into ▁and ▁out ▁of ▁the ▁cyl inder ▁is ▁one ▁way , ▁assist ed ▁by ▁blow ers ▁to ▁improve ▁cyl inder ▁exhaust ▁sc av eng ing . ▁The ▁in let / out let ▁port ▁order ▁is ▁In / Out / In / Out / In / Out ▁going ▁around ▁the ▁tri angular ▁ring ▁( i . e . ▁the ▁in let ▁and ▁out let ▁manifold ▁arrang ements ▁have ▁C 3 ▁rot ational ▁symmetry ). ▁ ▁Ear lier ▁attempts ▁at ▁design ing ▁such ▁an ▁engine ▁met ▁with ▁the ▁difficulty ▁of ▁arr anging ▁the ▁p ist ons ▁to ▁move ▁in ▁the ▁correct ▁manner , ▁for ▁all ▁three ▁cyl ind ers ▁in ▁one ▁delta , ▁and ▁this ▁was ▁the ▁problem ▁which ▁caused ▁J unk ers ▁Mot oren bau ▁to ▁leave ▁behind ▁work ▁on ▁the ▁delta - form ▁while ▁continu ing ▁to ▁prototype ▁a ▁diam ond - form ▁four - c rank sh aft ▁ 2 4 - cy l inder ▁J unk ers ▁J um o ▁ 2 2 3 . ▁Mr . ▁Herbert ▁Pen ward en , ▁a ▁senior ▁dra ug ht s man ▁with ▁the ▁Admir alty ▁Engineering ▁Labor atory , ▁suggested ▁that ▁one ▁c rank sh aft ▁needed ▁to ▁revol ve ▁anti - clock wise ▁to ▁achieve ▁the ▁correct ▁p ist on - ph asing , ▁so ▁Nap ier ▁design ers ▁produced ▁the ▁necessary ▁g ear ing ▁in ▁order ▁that