ORIGINAL: Sport_Pilot
The fuel has 23% thich synthetic oil. That is why they smoke so much. Nitro has nothing to do with it or you would not be able to see AA fuel dragsters and funny cars on the drag strip without a cloud of smoke behind them.
The nitro itself doesn't cause more smoke, true, but the richer mixture that comes with 20-30% nitro means you're flowing that much more oil at a given time. So in a way it contributes to more smoke indirectly.
At least that's how I see it anyway.