▁side . ▁ ▁As ▁a ▁two - stroke ▁dies el ▁engine ▁that ▁does ▁not ▁use ▁c rank case ▁asp iration ▁cannot ▁naturally ▁draw ▁in ▁comb ust ion ▁air , ▁the ▁blow er ▁is ▁inher ently ▁necessary ▁to ▁charge ▁the ▁cyl ind ers ▁with ▁air ▁for ▁comb ust ion . ▁The ▁blow er ▁also ▁ass ists ▁in ▁sc av eng ing ▁spent ▁comb ust ion ▁g ass es ▁at ▁the ▁end ▁of ▁the ▁power ▁stroke . ▁All ▁Series ▁ 7 1 ▁engines ▁use ▁un if low ▁sc av eng ing , ▁in ▁which ▁a ▁g ear - dri ven ▁Ro ots ▁blow er ▁mounted ▁to ▁the ▁exterior ▁of ▁the ▁engine ▁provides ▁int ake ▁air ▁through ▁cor ed ▁pass ages ▁in ▁the ▁engine ▁block ▁and ▁ports ▁in ▁the ▁cyl inder ▁walls ▁at ▁slightly ▁greater ▁than ▁atmos pher ic ▁pressure . ▁The ▁engine ▁exhaust s ▁through ▁push rod - oper ated ▁po ppet ▁val ves ▁in ▁the ▁cyl inder ▁head ( s ), ▁with ▁either ▁two ▁or ▁four ▁val ves ▁per ▁cyl inder . ▁Unit ▁fuel ▁injection ▁is ▁employed , ▁one ▁inject or ▁per ▁cyl inder , ▁with ▁no ▁high ▁fuel ▁pressure ▁outside ▁of ▁the ▁inject or ▁body . ▁The ▁inject ors ▁are ▁cy c led ▁from ▁the ▁same ▁cam sh aft ▁responsible ▁for ▁opening ▁the ▁exhaust ▁val ves . ▁ ▁N omen cl ature ▁ ▁The ▁first ▁number ▁refers ▁to ▁the ▁number ▁of ▁cyl ind ers ▁in ▁the ▁engine , ▁followed ▁by ▁a ▁hy phen ▁or ▁" V ", ▁indicating ▁inline ▁or ▁ve e ,