The added pressure wont have much difference on quantity, but can affect timing to some degree. I don't have a number as far as extra mm needed per 100psi increase or anything, but just from tuning experience they do like more timing with the higher pop pressures. If you stop and think how the pump works, it injects fuel based on the rotation of the pump since the cam plate drives the head/rotor assembly. While the diesel doesn't compress any measureable amount at these pressures, the pump does have to build more pressure to open the injector. To build more pressure, the rotor in the head will have to travel slightly further before that pressure threshold is reached. The slight difference in plunger travel equates to some degree in rotational movement of the pump shaft. Advancing the timing offsets that difference. I'm still very happy with my 273 nozzles I got from vwdieselparts.com. They are the chinese ones but are great quality. I've also built a set for Alex's car and they are running well for him too. I have had them in my car since last summer, and when I swapped the engine I checked them. Pop pressure was still the same and the spray pattern looked just as it did on install. They are selling for only $45 for a set of 4. He will sell you a set of six if you ask.
Jason
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