yep for the TB you defo need a 70mm hose mate which is the ID,as a rule alloy pipes are sized on there OD so still 70mm,only arguement you could have is that the ID of the alloy pipe is obviously a touch smaller than 70mm due to the wall thickness,(prob more like 67mm),personally can't see it making any difference
the maxogens that smoggy mark sells at the mo are 76mm OD (73mm ID) and apparently give better flow,i'm hopefully fitting mine tomorrow so i'll post some comparison pics comparing it to the standard 70mm maxogen (67mm ID) i run at the minute,you do need a 76 to 70mm reducer to run this though