[EdKiefer]

one drawback of roots blower is there no easy way to cool charge with a intercooler and you have no way to alter cam timing like new engines .
Modern 4 valve head chambers with center spark plug are also more efficient than older 2 valve wedge heads, can run more compression in general . Above features and direct injection the newer tech engines it starts to really add up on improvements compared to older engines .

The good thing on the newer breed of eco-turbo . I class eco -turbo as ones were there more for drive-ability then peak HP .they produce good gains in TQ at low rpms and are not peaky like older performance turbos . This gives a fat low rpm TQ curve (look at BMW TQ rpm range I posted link above its like 300ft/lb at 1400 rpm

On gearing my 08 Honda 2.4 5speed auto cruises at under 2k rpm doing 60 . Maybe older 3 and 4 speed needed to be gearing higher cause not so many gears . In Honda both 4th and 5th are overdrive ratio's .