Out of curiosity and to test the actuator for leaks I put an airsource and gauge on it and observed the following; 1st movement (starts to open) around 1.5 psi. Full movement 10 psi. I have about 2-3mm of pre load and a base boost of just under 6psi at 3.5krpm. So it doesn't take much (way under base boost) for the wastgate to start to open up and slow the turbo spool-up - thus why MBC's are fun. Remember this is also at the turbo outlet where I'm measuring so when you take into account losses in the IC and delivery pipe the WG is likely to be opening before it even registers on your dash gauge if the BPC valve is bleeding any pressure to it.