Well first off, it sounds like your BOV is bad. It should sound like a Pssst. Is it stock? What other mods have you done? Stock rims? Stock injectors-turbo-fuel pump-? Second of all if your useing a manual boost controler and you have a bad BOV then I say good luck. Not trying to scare you but spikes in psi are pretty common with the manual boost controller and if the air has nowhere to go then you have a bad problem. As far as how much boost to run, if your all stock(turbo-injectors) 12psi is about as far as you will get before Fuel Cut. But do your best and represent the SUPRA with PRIDE!!