Hey Dillz, the closer to throttle the better... it's set to leak off to atmosphere when things aren't right. My boost is set for 16psi, I'm guessing the overboost valve is set to open around 2psi over that. The ECU should correct boost, but I don't think it can react quick enough to situations like blowing a hole in cooler piping, splitting a rubber/clamp on pipes etc... doesn't take much to pop an engine when ECU thinks it's only using 5-7psi but the turbo is puffing at 25+psi to maintain a set manifold pressure, whatever it may be. It's pretty much like a safety relief valve on a pressure vessel, a preset boost pressure will still go through the throttle and to engine (in my case 16psi)... it just has the mechanical protection of the overboost valve so if 19+psi occurs it will be relieved to atmosphere... if this happens I'd say some noise would be heard in the engine bay