▁ 8 7 ▁oct ane ▁av iation ▁fuel ▁which ▁was ▁generally ▁available ▁from ▁ 1 9 3 8 ▁through ▁to ▁ 1 9 4 1 ; ▁from ▁early ▁ 1 9 4 0 ▁increasing ▁supplies ▁of ▁ 1 0 0 ▁oct ane ▁fuel ▁allowed ▁the ▁maximum ▁power ▁to ▁be ▁increased ▁to ▁ 1 , 3 1 0   hp ▁( 9 7 7   k W ) ▁with ▁an ▁increased ▁super char ger ▁boost ▁pressure , ▁al beit ▁for ▁a ▁maximum ▁time ▁limit ▁of ▁ 5 ▁minutes . ▁In ▁ 1 9 4 4 ▁ 1 0 0 / 1 5 0 ▁grade ▁fu els ▁enabled ▁the ▁Mer lin ▁ 6 6 ▁to ▁produce ▁ 1 , 8 6 0   hp ▁( 1 , 3 8 7   k W ) ▁at ▁low ▁alt itudes ▁in ▁F . S ▁g ear . ▁ ▁Single ▁stage ▁super charg ers ▁Depending ▁on ▁the ▁super char ger ▁fitted , ▁engines ▁were ▁r ated ▁as ▁low ▁alt itude ▁( e . g .; ▁Mer lin ▁ 6 6 , ▁Griff on ▁III ), ▁where ▁the ▁engine ▁produced ▁its ▁maximum ▁power ▁below ▁about ▁, ▁medium ▁alt itude ▁( Mer lin ▁ 4 5 ), ▁where ▁the ▁engine ▁produced ▁its ▁maximum ▁power ▁up ▁to ▁about ▁, ▁and ▁high ▁alt itude ▁( Mer lin ▁ 7 0 ), ▁where ▁the ▁engine ▁produced ▁its ▁maximum ▁power ▁above ▁about ▁. ▁As ▁a ▁result , ▁the ▁prefix es ▁which ▁were ▁used ▁on ▁most ▁later ▁Sp it fire ▁variants , ▁L . F