Hi Mike, I have a sweet running ZDZ 40 rv that is currently on this airplane. She weighs just under 15 lbs. I am using a 20/8 NX prop and I am totally satisfied with the airplane/engine performance. What I am not happy about is the need to re-tighten the prop bolts every few flights. (wooden prop hub compressing). I have an extremely delicate fiberglass spinner that can't tolerate too many more removals so I am wanting to install a Mejzlik prop thinking that the carbon fiber hub won't compress. Right now I'm turning anywhere from 7150 to 7300 rpm static with the NX prop and a Bisson side mount muffler. Would a Mejzlik 20/8 give the same performance or should I try a 21/8 Mejzlik?? Thanks

Go with the 21x8 Mejzlik, awesome. I would also recommend cutting the crimps off of the muffler downtubes to increase performance a bit more as well.
Thanks!