▁allowed ▁to ▁pass ▁through ▁the ▁inter co ol er ▁( in ▁addition ▁to ▁the ▁boost ▁supplied ▁by ▁the ▁primary ▁tur bo ). ▁Man if old ▁pressure ▁during ▁the ▁second ▁stage ▁of ▁tur bo charg ing ▁remains ▁reg ulated ▁by ▁the ▁primary ▁tur bo char ger ' s ▁waste gate ▁– ▁there ▁is ▁only ▁one ▁tur bine ▁by - pass ▁val ve ▁in ▁the ▁whole ▁system . ▁ ▁Sub aru ▁claims : ▁" The ▁' st aging ' ▁between ▁the ▁single ▁and ▁tw in ▁tur bo ▁operating ▁range , ▁which ▁was ▁quite ▁notice able ▁to ▁the ▁driver ▁on ▁the ▁previous ▁model ▁B 4 , ▁has ▁now ▁largely ▁been ▁' t un ed ▁out ' ▁by ▁the ▁careful ▁selection ▁of ▁tur bo char ger ▁size ▁and ▁the ▁cont rolling ▁mechan isms . ▁As ▁can ▁be ▁seen ▁from ▁this ▁tor que ▁curve , ▁however , ▁under ▁some ▁driving ▁conditions ▁it ▁is ▁still ▁possible ▁to ▁detect ▁a ▁slight ▁reduction ▁in ▁the ▁rate ▁of ▁acceleration ▁in ▁the ▁prepar atory ▁or ▁intermediate ▁phase ▁that ▁occurs ▁between ▁ 4 0 0 0 – 4 5 0 0 ▁r pm ." ▁ ▁The ▁Tur bo charg ers ▁ ▁Despite ▁being ▁called ▁tw ins , ▁the ▁B 4 ' s ▁tur bo charg ers ▁are ▁not ▁identical . ▁The ▁primary ▁tur bo char ger ▁is ▁an ▁I HI ▁V F 3 3 ▁unit , ▁which ▁uses ▁a ▁ 4 6 . 5 ▁/ ▁ 3 5 . 4   mm ▁ 9 - bla de ▁tur bine ▁wheel ▁and ▁a ▁ 4