If ya look up 26cc stihl or 27cc stihl in the search bar at the right hand lower corner on the thread page. youll come up with a few records.Stihl conversion[s] would also work.Heres a pic of my 28cc[27.2] actual.Im getting 7400 with a 17x8 APC at 3000msl.The 13mm would be to big i think.Im using a 10mm.