I dont think a 21 will turn one at that but i wont say it wont.Im pretty impressed with my stihls so far as for weight and power.My 28 in the pic above has a rail mount already like a glow engine and is spinning a 17x8 at 7400 at 3000 Ft msl and i bought it used.It weighs 3.5 lbs with evrything rtf.Besides ign battery.Im sure your right its just a different motor.Its probably some stroker motor that came off of a special purpose item that is no longer built.Could also just be older like the echos that used to have round cylinders.If anything runs like that and its light who cares who makes it.I might see how fast i can get one of my 22cc done to see what it does,with EI.