Small engines give off their heat very quickly and DO need higher nitro fuel to keep the temp up. Cox standard blue can fuel was 25% nitro and the red can racing fuel was 35% nitro. Both use 20 castor oil. They will run on 10% but don't like it. World of difference with high nitro. K%B made Super Sonic 1000 with 25 % nitro for 1/2 A engines.