Alright, all vaccum lines use a neg. presure so how does it all work when you have a turbo putting pos. presure on them? If the vaccum is gone during boost what keep the positive presure from going up then vaccum lines?

 

nothing does, you just dont have any. a good example is with the brake booster, while under boost conditions you car had no vacumn for brakes but thats where the pvc valve comes in place, it keeps a certain amount of vacumn in the booster for at least one good stop