ORIGINAL: skydevil1
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.
Here in the US we naturally use fuel with nitro but there are many countries where you simply cannot do this and they run theirs on zero nitro. Hard for me to imagine but they do it because they have to or else go diesel.
Robert