Brian,


The prop size chart (and the rest of the English language manual) is a direct translation from the Italian language manual.

No prop size larger than the 11x6 is slated for the .51.

I don't know what pamphlet you got with your engine, but it contradicts the original Italian Super Tigre document.

Please look at [link=http://www.rcuniverse.com/forum/m_2204148/anchors_2204148/mpage_1/key_Super%252Ctigre%252Crpm/anchor/tm.htm#2204148]this thread[/link].

This engine obviously has a huge hole in the torque curve, just above 10,000 RPM.
If the prop is light enough to sail over this hole, as would a 10x6, it will go to 14K+, but if not, like the 11x7, you've got a bogged engine...

Some other engines in this size bracket, namely MVVS and Irvine, are happy with larger props, even a 12x7 will not bog them down.