I just got back from the field after running the engine. Wow!!!! I am blown away with it. Super smooth, it is without a doubt the smoothest single I have ever run. I ran about 36 oz of fuel through it and tested three props. I was running the stock Zenoah muffer which I have read in many places really restricts the rpm. With the muffler on I ran a Xoar Sword 22x8 at 7180. The Xoar C.F. 22x10 was 6600 and a Falcon Beach 22x10 was 6200. All props were re-tuned for mixture. Then I removed the muffler and re-ran the Xoar C.F. 22x10 and got 7120 rpm. An increase of 520 rpm. In past tests I found most side dump mufflers fell between 50 to 100 rpm loss depending on the muffler. The wrap around ones I tried in the past fell between that and 300 rpm loss depending on the brand. I am going to be using a Jtec wrap around on the plane this engine so I am expecting that to put me right on 7000 rpm and then what ever I gain as it breaks in.
BTW all rpms were taken on a heat soaked engine....