Turns out that Just Engines got a shipment of ASP .91 2 strokes in. As I had never cancelled an order that I put in back in June, they sent one out to me this week. I intend to mount this engine on my Vector Flight Extra 66". The plane weighs about 8.25 pounds. What prop would you recommend for this engine?

13x6-8, 14x6-8, 15x6

I run 14x8 APCs on my ST 90 in a Midwest CAP 232, turned 9000 when it was still pretty new, believe it is higher now. Flies the plane very well....somewhat quiet by higher pitch and lower rpm, good speed for point rolls and knife-edge, and adequate vertical. Same results with a GP Extra 300 and a Magnum 91, the previous version. I don't do 3D or a lot of the hovering type stuff so you would want to go up in diameter and down in pitch if that is your thing....

Clair

I don't know the rating numbers for your new motor, but I have a YS .91 which turns an APC 15x6 at 9750 RPM. I am spinning it a little fast, but it has great performance. I may try a APC 15x8 to see if that will slow the RPM's down to around 9300 RPM, plus should give more thrust. YS makes a little extra HP compared to other engines in the same class, so you may want to go with a 15X4, 14x8 or 14x6. I had a APC 14x6 which I turned over 11000 RPM with. WAY TOO FAST!!!, but you just have to get several props to find out which is best for you and your style of flying. If you want speed, go with a lower diameter and a higher pitch. If you want more thrust, then go with a higher diameter and lower pitch. The choice is yours depending on your style of flying.