It's clear that the higher the max RPM is more HP should follow. However, whats the relationship between HP/Liter and Max RPM? Below is a graph using EVO Data. I added whether the car was has some sort of forced induction or whether it was naturally aspirated.
From the graph there are two separate relationships for naturally aspirated engines and forced induction engines. Naturally aspirated engines have to rev much higher to achieve the same hp/liter ratio. In addition the naturally aspirated observations have a much more linear relationship than forced induction counterparts.
With all thats being said about the death of manual transmissions and the increasing ubiquity of electric steering I'm surprised people aren't talking about takeover of forced induction engines over natural breathing. Higher revving engines can be more fun (as I claimed in my last post). And if turbos can't give us that same stratospheric rev range that natural aspiration can do, should we shun the take over of the turbo as well?