I'll give you the philosophical argument, you guys can talk technical.

IT head prep is the cornerstone of three categories: Improved Touring, Super Touring (Light), and Limited Prep Production. All were created to try and minimize modifications in a (Sysiphian) goal of minimizing expensive modifications.

Unless and until we are willing to move STL into a realm of prep similar to Super Touring Under (e.g., porting, bigger brakes and tires, sequential gearboxes) and/or full-prep Prod (which is on the wane due to costs) then I suggest porting does not have a place in the class. and as/when we do that, it moves further toward reducing the differentiation of the class from other existing classes.

GA, "The Philosophy Guy"...