ly ▁known ▁as ▁disp lacement ▁on ▁demand ▁( Do D )) ▁is ▁a ▁tra dem ark ed ▁name ▁for ▁the ▁autom obile ▁variable ▁disp lacement ▁technology ▁from ▁General ▁Mot ors . ▁It ▁allows ▁a ▁V 6 ▁or ▁V 8 ▁engine ▁to ▁" turn ▁off " ▁half ▁of ▁the ▁cyl ind ers ▁under ▁light - load ▁conditions ▁to ▁improve ▁fuel ▁economy . ▁Est im ated ▁performance ▁on ▁E PA ▁tests ▁show ▁a ▁ 5 . 5 – 7 . 5 % ▁improvement ▁in ▁fuel ▁economy . ▁ ▁G M ' s ▁current ▁Active ▁F uel ▁Management ▁technology ▁uses ▁a ▁sol en oid ▁to ▁de activ ate ▁the ▁lif ters ▁on ▁selected ▁cyl ind ers ▁of ▁a ▁push rod ▁V - layout ▁engine . ▁ ▁Background ▁High - power ed ▁multi - cy l inder ▁internal ▁comb ust ion ▁engines ▁may ▁be ▁necessary ▁to ▁satisfy ▁driver ▁dem ands ▁for ▁quick ▁acceleration ▁and / or ▁heavy ▁to wing ▁capacity , ▁but ▁during ▁daily ▁use ▁they ▁are ▁generally ▁operated ▁at ▁power ▁settings ▁of ▁less ▁than ▁ 2 5 %. ▁For ▁example , ▁at ▁fre ew ay ▁( mot or way ) ▁spe eds , ▁less ▁than ▁ 4 0   hp ▁( 3 0   k W ) ▁are ▁required ▁to ▁overcome ▁aer od ynamic ▁drag , ▁rolling ▁fr iction ▁and ▁to ▁operate ▁access ories ▁such ▁as ▁air ▁condition ing . ▁ ▁However , ▁when ▁a ▁gas oline ▁( pet rol ) ▁internal ▁comb ust ion ▁engine ▁is ▁operating ▁under ▁less ▁than ▁full ▁load , ▁the ▁effective