My CC was delivered with a 55 pitch cruise prop. Over the winter I added the new cowl flaps and changed to the new metal edge prop at the same time moving from a 55 pitch cruise prop to a 54 pitch.
Before these changes I documented my POH max power cruise speeds. I am now flying with the new prop and the new cowl flaps in the full open position (most drag). My CC is now flying 4 mph faster. Before the prop and cowl flap changes I would nominally see 88 mph on an ISA day at 1,000' MSL burning 5.1 gph. Same conditions I am seeing 92/93 mph now.
Makes no sense. Both the prop change and cowl flap change should yield slower speeds. Wonder if there is some special stuff on these metal edge Cato props?
BTW, I have calibrated my TAS against GPS per this procedure. My TAS is only 1 mph slower than actual based on this calibration. So this speed increase is real, not measurement error.