if you did a search, you would realise that:
the gauge reads in mmHg, NOT psi or bar, and this means that +7 is approx 14psi or just under 1bar
so on a stock R33, the boost should reach about +3.5 at full boost. an exhaust and air filter might lift this to about +4 or +4.5, but the only way for it to reach much higher is using a boost controller...
Warren.