I would venture that the 75 Zenoah is slicked up a little to produce good performance at 11 grand?
My limited experience with this engine at 5--6000 rpm showed very limited performance -
I was only an observer/flyer - but it sure seemed like it was very meek.
My friends who run the 80 agree - these are quite tame in stock form.
Have you come up with any mods that wake these things up --in the 6000 rpm range?