Here is a thread that talks to this topic. http://www.rcuniverse.com/forum/m_17...tm.htm#1733757

Ralph Cunningham (RCIGN1) is an expert on Zenoah engines. He converted a G26 to electronic ignition for me and it is the best running engine I have. I think you will find that you are right on the limit of where you should run this engine and that a larger prop is needed to convert those rpm into thrust.