Another component to this is the DI rail pressure itself, and the slight pressure drop that occurs during the injection event. Take a look at Deatschwerks injector data, it seems that looking at rail pressure alone isn't enough, since the Ecoboost 1700cc injectors have different slope values at the same pressure, depending on the engine. The only reasoning I can come up with for this is that a better HPFP will be better at displacing the fuel mass in the rail for the next injection event (ie. less pressure drop). So it's very possible in my mind that an upgraded pump with the same commanded rail pressure and injection timing could deliver a higher volume of fuel than an OEM pump.

I haven't quite wrapped my head around how one would "correctly" tune for an upgraded HPFP and injector combo without values from the manufacturer, given that it seems to inadvertently affect the injector data.

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