I can't even touch this, but I might just learn somethin'. :idea:
Someone from the highly experienced "old guard" who have been running and tuning jets for decades I am sure will come and educate both of us. I have been told the same thing, by DuaneHTP, but didn't ask for an explanation at the time. I'm sure a lot depends of setup. If an engine is being held below it's best power, an impeller cut will make it faster as the engine can now wind up to it's power, allowing more pump pressure to build. Beyond that obviousness, I'm gonna sit back & get a lesson.