Hello. My father in law has a GN with a TA-49 turbo, w-09 injectors, upgraded chip (has letters TT on it), adj fuel pressure reg and upgraded fuel pump. He is at 15-17lb's of boost. His tuner says he can turn up the boost to 25lb's safely with no other mods. What is the consensus on this. He is new to turbo cars. Thanks in advance.