I am curious, does the HKS SSQV use different level springs for different levels of vaccum, similar to the Tial BOV, or does it not use any spring because of its dual valve design?

Also, with regard to BOV springs, how does one size the spring? Is it supposed to be equal to the level of vacuum, once warmed up, at idle?

 

It uses a standard spring that is adjustable from the back, though it is limited. It is not a based upon the vacuum of a certain application.