It turned in the 8s, I can't really recall, it's been a while but the big prop does drop the rpm quite a bit. I still have a couple of the OS 91s but I use the YS 110s instead most of the time these days. In the Kaos I started with an MDS 68, then went to a YS 110 then put in the OS 91. The OS ended up staying in the plane for a number of years, it turned out to be the best combo for the plane. I have a good tach but once I find the prop I like and have the engine in tune I keep using the same size prop and never touch the needles again except when our temps drop. From summer 115 degrees to winter mid 20s the high end changes about 4 clicks. When I find the props I like I buy about 4 of them, balance and put in my flight box. I only use the tach on the first tune just to get the engine set, about 400 rpm fat. I never write what it is down, doesn't mater to me as long as the engine runs perfectly.