▁becoming ▁too ▁hot ▁and ▁either ▁ign iting ▁before ▁reaching ▁the ▁cyl ind ers ▁( pre - ign ition ▁knock ing ) ▁or ▁creating ▁a ▁condition ▁known ▁as ▁knock ing ▁or ▁det on ation . ▁The ▁inter co ol er , ▁which ▁was ▁separate ▁from ▁the ▁engine ▁cool ing ▁system , ▁with ▁its ▁own ▁supply ▁of ▁g ly col ▁and ▁water ▁cool ant , ▁was ▁mounted ▁in ▁the ▁induction ▁system , ▁between ▁the ▁out let ▁of ▁the ▁second - stage ▁super char ger ▁and ▁behind ▁the ▁cyl inder ▁blocks . ▁The ▁hot ▁air - f uel ▁mixture ▁from ▁the ▁super char ger ▁was ▁circul ated ▁though ▁and ▁around ▁the ▁cool ant ▁tub es ▁and ▁was ▁then ▁passed ▁on ▁to ▁the ▁main ▁induction ▁manifold , ▁through ▁which ▁it ▁was ▁fed ▁into ▁the ▁cyl ind ers . ▁The ▁inter co ol er ▁also ▁circul ated ▁cool ant ▁through ▁pass ages ▁in ▁the ▁super char ger ▁cas ing ▁and ▁between ▁the ▁imp ellers . ▁Finally , ▁an ▁extra ▁radi ator ▁( mount ed ▁in ▁the ▁star board ▁radi ator ▁du ct ▁under ▁the ▁wing ▁of ▁the ▁Sp it fire ) ▁was ▁used ▁to ▁diss ip ate ▁the ▁inter co ol er ' s ▁excess ▁charge ▁heat . ▁ ▁With ▁the ▁two - stage , ▁two - speed ▁super char ger , ▁two ▁sets ▁of ▁power ▁ratings ▁can ▁be ▁quoted . ▁As ▁an ▁example , ▁the ▁maximum ▁power ▁generated ▁by ▁the ▁Mer lin ▁ 6 1 ▁was ▁ 1 , 5 6 5   hp ▁( 1 ,