Nitro fuel is so called because it contains nitromethane (amongst other things, notably oil and additives). Higher nitro content generally means higher explosive content within the rc fuel. However, that doesn't necessarily translate into higher performance from your RC nitro engine. Generally we at Wheelspin Models recommend 16% - 20% nitro for .12 - .18 size nitro engines and 25% for .21 or larger nitro engines. The most important thing to remember is to stick with a good quality brand of RC nitro fuel such as HPI Optifuel or Byron.