OS .91 FX ringed. OS recommends a 13/8 or 13/9. This is a sport plane application. I do not know the recommended RPM range for this engine. This engine has been tached with the following results:
13/6 @ 12,500
13/8 @ 10,400
13/10 @ 9,500

14/6 @ 10,900
14/8 @ 9,500
14/10 @ 8,400

15/6 @ 10,200
15/8 @ 8,100
16/6 @ 8,300

From what I've read a 14/4 works well with this setup. With a 13/6 @ 12,500 and a 14/6 @ 10,900 a 14/4 should put you in the high 11,000s. Go APC over wood. Joe