This is a email from the Horizon hobby product support, that sale the alpha Evolution trainer engine. The company emailed it to me today. I've been running the 11x7 prop, with good performance.


We would recommend using either a 10x6 or an 11x6 prop for this engine. I
hope that you have found this information helpful. If you have any further
questions please feel free to contact us at 1-877-504-0233.

Sincerely,
Horizon Product Support