i fly helis so when i bought my gt 10 with the tt.15 engine, so i am just using the 15% nitro heli fuel , i think its running fine mabey just not as much speed, runs cool and pretty fast after about 8 tanks, another other worries i should think about .

I would definitely consider running nitro fuel intended for cars instead of helis. It's probably better on the engine. Most people buy about 20% nitro fuel most of the time.

some nitro engines only require 15% nitro, so you are okay on that part. 20% gives you more power (punch)

Your concern would be the lubricant %. (oil content). Just make sure its enough for the eninge requirements. (I think 15% lubricant is common).

http://www.*********.org/understanding_fuel.htm