Unless the SV-11 is really heavy, the 13-5 might not be enough prop. Either way, you should try a 13-6. This is the most common size prop used on St.60 models I think that weigh 60 ounces or more. When I first started to gain experience with a Tom Lay ST.60 it was in a 72 ounce Cardinal full fuselage model. That's a lot of airplane! I gathered up several different 13-6 props to experiment with, including the very hard to find Rev-Up 13-6 that some consider the gold standard as a prop for this engine. I tried Zingers, Brodak, older Top Flite and some plastic props. What worked the best was the Brodak 13-6. When a ST.60 is propped correctly, it just has a certain sound that it makes, and this helps in telling you you have it loaded correctly. The Cardinal was marginal at best with this combo, and then I read about the Vess brand props in a Flying Models article by Allen Brickhaus and got a few of them to try. On the morning of the test,. I made two flights with the Brodak, recording t he fuel used, RPM, lap times and run times as a base setting. Then I put the Vess prop on and the same load of fuel, and had to open the needle a bit for the same take off RPM. On starting it, it made that special sound! The exhaust note is just very distinctive. When I flipped it over after starting it broke into a nice two stroke and went back to a nice steady run when level again. It pulled MUCH better than the Brodak prop, and with some more trimming and practice with the model it could have been used in contest work. I acquired a new model from Sparky a few years ago that is much lighter (60 ounces), about the same size, and have that same engine in it. Since the experience with the Cardinal Xoar brand props have become available. I got a few examples of the 13-5 and 13-6 and did some test flights, and these props work very well also. I think they work much better than the Rev-Up 13-6 that is legend for this engine. Get yourself a couple of each, and a Brodak 13-6 and do some test flying. Give us some more detail such as model weight, line length, fuel and plug also.
  Type at you later,
  Dan McEntee

   I don't know about peak RPM, I have never pushed a ST.60 that far, even on a 72 ounce Cardinal!  For a model that size and with a 13-5 prop, you might be in the 800 t 8500 RPM range, a bit less with a 13-6. run that thing on a test stand some more with no muffler, at about 75oo RPM and see how the exhaust comes out, clear or with a slight brown castor tint, or dark. If it's dark, that is metal coming off the rings yet. It usually doesn't take very long for a ring to seat, you just don't want to push on a stand. use a 12-4 prop or an old 13-5 cut down to 12 inches. Take a look into the exhaust and see what the ring looks like. It should show a shine going from the top of the ring down as it seats. If you see it shiny just at the top, it's still seating.  I was flying today and flew my Atlas with that ST.60 in it I was referring to, and I think I have a Xoar 13-5 on it and take off RPM was 8000 RPM and gave me a 5./4 lap time. I just don't remember what the line length is I was using, but might be in the 65 feet range handle to model center line. I run Glow devil R/C long with idle bar for a plug. I'm not really familiar with OS numbering system but they changed it a few years ago. If it is from recent times, some of there plugs aren't full length for along reach plug, and the end might not be all the way into the combustion chamber. See if you can get or borrow a Glow Devil or a Thunderbolt R/C Long with Idlebar, or the Thunderbolt 4 stroke plug. You want a hot plug. Fuel should be at least 20%  total oil with at least half castor and I think Riches Brew is. We used to be able t get it here in St. Louis and it's similar to the SIG 10%  Champion I use. If you are still breaking in, add a few ounces of castor oil to it, or a few more ounces of Klotz if you have it. Let us know what you find out.
   Type at you later,
   Dan McEntee

Thanks guys. I’ll pull it out of the plane and play with it more on the test stand.
I only peaked it to get an rpm to compare with and old beater ST 61 that I was going to give to one of the local guys. I didn’t want to give him a junker as it’s going in one of my old SV11 s that I crashed. I figured if they both turned the same prop at similar rpm, it should be good to use.

Matt

Theres the olde ' trim down a 14 inch prop ' trick , too .