yes both s/c and na have the 1.6 ratio. now the reason why zzp has split ratio rockers because 1.9 can actually hurt hp numbers on a n/a car. theres two ways to get more flow...1. increase the pressure of the air going into the engine or opening up the intake path. rockers would be like opening up the intake path more. Now a certain rocker ratio is optimal for n/a cars that happens to be 1.84 and 1.8 because the 1.9 opens more is also slows the air down because your loosing pressure and this equals less hp. And yes you can put 1.9s on a n/a. the
