Why Is It Called 'Top Fuel'?
The people who built the predecessors to Top Fuel cars—engineers, mechanics and amateur drag racers around the world—eventually came to the conclusion that a nitromethane blend is the best type of fuel for these particular types of engines. Nitromethane is also known by its chemical makeup, CH3NO2. It's a dangerous and volatile substance that's often used for pesticides, medicine manufacturing, heavy duty cleaning solvents and even rocket fuel. Nitromethane burns at a relatively slow rate compared to other fuels, and some unburned nitromethane may escape through the exhaust system and ignite when it comes into contact with the atmosphere, resulting in the exhaust pipe flames that contribute to the spectacle of a Top Fuel race.
An engine that runs on nitromethane is typically much lower compression than a gasoline engine [source: Davis]. Unlike gasoline, nitromethane carries oxygen, so the engine doesn't need to force in as much air for the combustion cycle, allowing it to run at lower compression. Still, all of the connections need to be inspected and repaired on a regular basis. For example, the welds on the custom headers start to fail after about 50 or so runs [source: Mazlumian]. If a Top Fuel car's engine is not running properly and unburned fuel builds up in the engine, it can explode with a force strong enough to crack the engine's head or block.
Currently, Top Fuel run on a blend that's 90 percent nitromethane and 10 percent methanol, according to NHRA rules [source: Davis]. The methanol helps suppress detonation, which makes the fuel more stable. The fuel is tricky to blend at the proper ratio because it's mixed by weight, which depends on its temperature. And to further complicate matters, the fuels themselves can vary in purity by a few percentage points. Blending top fuel for stability and premium power can yield varied results; in most cases, the fuel works as intended. Nitromethane can be blended with substances other than methanol to help boost its power potential, but such tactics are banned by the NHRA and most other racing organizations, in part because other fuel blends are more dangerous and also harder to regulate.