I have been using O'donells 30% nitro in my two r/c cars I race, well I got tired of paying 40.00 a gallon and said I'll try some traxxes 33% nitro fuel, Well first thing that happens to both vehicles one a 4-stroke truggy with a saito 125 in it , and the other a standard 2 stroke in an associated SC-8. well they both drop about 35 to 40 degrees in run tempature with a lower Idle. this is great but I'm wondering what the heck is the difference in the fuel. anybody have a clue?

Some fuel manufacturers mix by weight instead of volume. In comparison a fuel mixed by volume will have a higher nitro content. Higher nitro more heat. Also Traxxas does not publish oil content percentages.

Nitro evaporates faster  so with higher nitro content you end up with a cooler motor.

Methanol evaporates easier and faster than nitromethane. The previous post is incorrect. Except for speed and a few other events, most people use much more nitromethane than their engines require in the U.S. Sometimes people will go from 10% nitro to 30% nitro to get a few hundred more rpm, sometimes less. For example, the Saito engines will run fine on 10-15% nitromethane. I am NOT talking about contest flying, competition and the like. I am talking about sport flying. In other countries, often nitromethane is not available, or even illegal to possess.