Originally Posted by matthart

As I understand it, at 1 BAR boost the ECU will be doing the fuelling based on the 1:1 (standard) regulator, so it will be expecting the fuel to be at 4 BAR (3 BAR idle + 1 BAR), and on the chip will be an amount of "squirt" for that pressure, whereas with a rising rate jobby, it will have the fuel at something like 4.5 BAR, so for the same "squirt" you will get more fuel than expected.