i rescently turned the boost up from 5psi to a still conservative 8psi on my 84 300zx. unfortunately my car is now slower because of what seems to be fuel cutting off or timing being retarded. i was told that Z31's could take 10-12psi on stock fuel system, but it seems not the case... not sure what it is. if anyone knows please share the info.

 

you have another problem.

1) bad mafs
2) bad fuel pump
3) bad fuel pressure regulator
4) vacuum leaks
5) incorrect timing

 

I assume the Injector recall from Nissan has already been taken care of ? I would check your fuel pressure and timing.