ust ion ▁ch amb ers . ▁Ex pected ▁power ▁was ▁to ▁be ▁ 6 5 - 7 5 hp ▁for ▁road ▁b ikes , ▁and ▁at ▁least ▁ 1 0 0 hp ▁for ▁the ▁racing ▁b ikes . ▁ ▁The ▁P 8 6 ▁had ▁a ▁bore ▁of ▁ 8 5 . 6 mm ▁and ▁a ▁stroke ▁of ▁ 6 4 . 8 mm , ▁giving ▁a ▁capacity ▁of ▁ 7 4 6 cc . ▁A ▁timing ▁bel t ▁was ▁used ▁to ▁drive ▁the ▁c ams , ▁rather ▁than ▁the ▁g ear ▁train ▁used ▁on ▁the ▁D F V . ▁The ▁P 8 6 ▁shared ▁the ▁same ▁comb ust ion ▁chamber , ▁head ▁designs , ▁p ist ons ▁and ▁ro ds ▁from ▁the ▁D F V . ▁ ▁N orton ▁specified ▁that ▁the ▁P 8 6 ▁must ▁run ▁through ▁a ▁single ▁car b ure tt or ▁source , ▁which ▁led ▁to ▁a ▁ 3 6 0 ° ▁firing ▁interval , ▁with ▁both ▁p ist ons ▁rising ▁and ▁falling ▁as ▁a ▁pair . ▁As ▁this ▁led ▁to ▁increased ▁v ibration , ▁a ▁dual ▁counter ▁bal ancing ▁system ▁was ▁developed , ▁in ▁conj unction ▁with ▁a ▁heavy ▁fly w heel . ▁In ▁an ▁engine ▁we igh ing ▁ 1 9 5 ▁l bs , ▁ 7 5 ▁l bs ▁of ▁that ▁was ▁a ▁rot ating ▁mass ▁inside , ▁which ▁was ▁a ▁lot ▁of ▁in ert ia ▁for ▁the ▁engine ▁to ▁overcome . ▁ ▁The ▁P 8 6 ▁had ▁dow nd ra ug ht ▁ports ▁like ▁the