ST class cars have to ur the OEM calipers for their car. Pads are open as log as they fit the oem caliper and approved rotor.
In GS we are allowed a slight front rotor diameter increase over stock rotors.
We are also allowed a 4 piston 2 piece caliper on te front and need to run a factory or approved rear caliper and brake pads are open. GS class cars are also allowed an approved racing ABS system.
Part of the uproar in GS this year is the addition. Of the Z28. It is not really suppose to be in GS as its way too much car for the class...hence the magazines compare it to the GTR and Porsche GT3.
We are not a GTR
The Z28 showed up at Daytona with 6 pistonAP racing front calipers and 4 piston AP racing rears... 6 piston calipers are not legal for GS... But somehow they got approved on a car that has a 7 ltr v8 also.
Rule # of racing... Politics