The OS 40 LA's like anywhere from 5%-15% nitro. Use a fuel that has some castor in it. As for total oil content this is debateable depending on which fuel you are using. Some fuels have a higher viscosity oil in them so you might not need as much oil. I always use Wildcat 15% nitro, 18% totaly synthetic oil, then add about 4 oz. of Klotz Castor to it to bring the oil content up to 20%. This may be overkill, but I haven't had any problems due to lack of oil, and the engine (OS 46 SF in this case) has plenty of power.