inder ▁and ▁cyl inder ▁head ▁spaces ▁at ▁the ▁top ▁of ▁the ▁stroke . ▁The ▁gas ▁in ▁this ▁" de ad ▁space " ▁will ▁expand ▁during ▁the ▁next ▁induction ▁stroke , ▁and ▁only ▁after ▁it ▁has ▁dropped ▁below ▁the ▁supply ▁gas ▁pressure , ▁more ▁supply ▁gas ▁will ▁flow ▁into ▁the ▁cyl inder . ▁The ▁ratio ▁of ▁the ▁volume ▁of ▁the ▁cyl inder ▁space ▁with ▁the ▁p ist on ▁fully ▁with dra wn , ▁to ▁the ▁dead ▁space , ▁is ▁the ▁" com pression ▁ratio " ▁of ▁the ▁boost er , ▁also ▁term ed ▁" boost ▁ratio " ▁in ▁this ▁context . ▁E ffic iency ▁of ▁the ▁boost er ▁is ▁related ▁to ▁the ▁compression ▁ratio , ▁and ▁gas ▁will ▁only ▁be ▁transferred ▁while ▁the ▁pressure ▁ratio ▁between ▁supply ▁and ▁dis charge ▁gas ▁is ▁less ▁than ▁the ▁boost ▁ratio , ▁and ▁delivery ▁rate ▁will ▁drop ▁as ▁the ▁in let ▁to ▁delivery ▁pressure ▁ratio ▁increases . ▁ ▁D elivery ▁rate ▁starts ▁at ▁very ▁close ▁to ▁swe pt ▁volume ▁when ▁there ▁is ▁no ▁pressure ▁difference , ▁and ▁dro ps ▁stead ily ▁until ▁there ▁is ▁no ▁effective ▁transfer ▁when ▁the ▁pressure ▁ratio ▁reaches ▁the ▁maximum ▁boost ▁ratio . ▁ ▁Com pression ▁of ▁gas ▁will ▁cause ▁a ▁rise ▁in ▁temperature . ▁The ▁heat ▁is ▁mostly ▁carried ▁out ▁by ▁the ▁com pressed ▁gas , ▁but ▁the ▁boost er ▁components ▁will ▁also ▁be ▁he ated ▁by ▁contact ▁with ▁the ▁hot ▁gas . ▁Some ▁boost ers ▁are ▁co o led ▁by ▁water ▁jack ets ▁or ▁external ▁fins ▁to ▁increase ▁con ve ction al