i just got a 93 s13 with an sr20det with a T28 skyline turbo..

1. My boost is 7psi low and 13psi high.. shouldn't i be able to boost higher than that somehow..???

2. When i put it on 13psi it likes to detonate, I can do 12psi safetly any suggestion or answers..??

Really need help i want to make this car perfect i just got it yesterday..