[v8volvo]

Right, that is certainly true, and I suspect that in addition to retarding effective in-cylinder timing the higher breaking pressure also causes less total volume of fuel to be injected for a given setting of pump piston travel (aka the "smoke screw"). Both of these can be compensated, by altering pump timing and increasing injected quantity by turning in the screw.

Better fuel atomization is the intended result, and there is a reason that in the case of our modified engines the normal TD setting value of 155 bar might not be high enough. Part of my rationale for running the higher injection pressure is that ultimately this engine will be ending up with higher in-cylinder pressure right before the moment of injection, due to increased airflow and manifold pressure. The combination of the upcoming changes -- D24 cam with earlier lift and longer duration, D24 intake that flows more air, larger turbo/increased boost, intercooler -- will all ultimately have the effect of cramming more air into the cylinder, and when it is compressed it will mean that there is considerably higher pressure in the combustion chamber for the injector to overcome as it begins to spray the fuel in.

You want the pressure differential to be a given ratio for optimum atomization. Making the fuel/air pressure ratio greater (as in higher injection pressure at a given in-cylinder pressure) is fine for atomization, but increasing combustion chamber pressure without also increasing injection pressure is a recipe for compromised atomization, which leads to more smoke, less power, worse efficiency etc when running under boost. This is the same reason there are different specs for setting breaking pressure on D24T vs NA D24 engines. Higher compression pressure and more air volume requires higher injection pressure or else complete atomization will not occur. That is why you can run turbo injectors in a NA engine, but it is not a good idea to run NA injectors in a turbo car.

So, short story is that when I was building the injectors I anticipated the fact that in the future I intend to increase the amount of air and compression pressure in my cylinders, and figured I should therefore slightly increase the injectors' breaking pressure as well to keep their pressure differential closer to what was intended.