None, if going along at cruise and change MP from say 24 to
to 20,eng just gets slight softer.Have had a number of desents where MP climbed from 20 to 24 and I never audibly noticed, RPM setting changes are very noticible , infact can set eng closer to 2400 by ear then with the gauge. I use didital point at prop tac for long cruise.
Plane is down right now, installing inverted oil. Wanted to jump back in and pay real attention to volumn change.
Also I rember distenctly after my spiner exploded and was at ideal and cruise speed. I had to realy listen if engine had restarted when I added mixture. Wasn't positve untill move throttle some.
HiTech