The two props you should try are the 13-8 and 14-6, preferably APC but all brands and types should work. I would think the 14-6 should work well. If you are haveing detonation problems with a 13-8 then either you are using too much nitro, too hot a plug, or you do not have the choke adaptor attached. Without the choke adaptor the engine will lean out in the air, and have problems with running too lean and if you richen it up will have strange transition problems, smaller propes will increase engine speed and velocity through the carb, resulting in better fuel draw, but to use the props you need for this engine you will need to use the choke adaptor. This is not the same as on other four stroke models. If you look at the choke adaptor on an OS or Saito you will find that it is the same or larger size than the carb bore, but on the TT the choke adaptor has a smaller size than the carb bore and this restriction allow's the carb to draw fuel.