I think 16 is a safe number without a tune or any type of wideband gauge fitted to the car . Anymore you need to start looking at other mods to be 100% safe .


Gc8s aren't the youngest kid on the block anymore so take this into account when doing mods. before touching the boost if it hasn't been done replace your fuel pump with a decent aftermarket unit . This at a minimum before I would even consider 16 psi .