Then how do you know the noisey bits on the wing are going to produce rated power! maybe its just done when you arn't around!
One of them has just been through the turbine enhancement for the B17, and on the bench both got over 500 hp! (according to standard aero)
But we do have a "poor mans" trend monitoring program in place to monitor engine performance and we do engine ground runs, as required, and under supervision of the CEO.. (well he does own them as well, so he doesn't want to see them break!)