I'm no injector expert. I belong to a forum competition diesel. I have a 1994 dodge cummins. I know that setting pop pressure does in fact change timing. Most everyone in the diesel performance side does up the pressure. I can say from experience changing pop pressure is a good thing. I had some stock injectors with low miles at 260 bar. They idled horrible and wasn't running good. I had a new set of nozzles 200hp over stock set at 290 bar. It idles way smooth and runs great. Fuel pressure does play a large role too in the cummins inline pump. Stock pressure is around 20psi. The higher pressure helps fill the pump plungers. General 50psi or so at wot is a good rule of thumb. Hope this helps.