I'm running my Zenoah 26 ei with a Master-airscrew Classic 18x8. I forget the rpm, but it sure pulls my Hangar 9 1/4 scale cub around really well. I look forward to every flight. I flew this setup after the 2nd tank, it is one of the easiest to start and setup engines I've ever had. I tried a Top Flite 18x6 wood prop and did not like it at all. I may try a 17x8 for a quicker spool up, but it's a Cub it already has tons of power without high speed. Hope this helps.

Wilki