Some years ago ABC WideWorld of Flying did a demonstration with a C-182.
He demonstrated both glide ratios and minimum sink with engine at idle, engine idle with prop in course and fine positions and with the prop stopped.
Results were very impressive. If I'm remembering correctly, delta between engine at idle, prop at fine pitch and prop stopped, the glide improved something like 26%.
I'm pretty sure I still have the tape. I could dig it out and run it again.
Mel Asberry..DAR since last century
A&P/EAA Tech Counselor/Flight Advisor
Specializing in Amateur-Built and Light-Sport Aircraft
North Texas (8TA5)
RV-6 Flying since 1993, 172hp O-320, 3-Blade Catto (since 2003)
Legend Cub purchased 12/2017
FRIEND of the RV-1
Eagle's Nest Mentor