Nitromethane has been called chemical supercharging because oxygen is part of its chemical
This slightly viscous liquid was originally created as a solvent for use in the dry cleaning industry. Its first use in competition is shrouded with various first-use claims, but among the accomplishments of record is nitro's first successful use in a circle track Midget driven at the famous Gilmore Stadium in 1950 by future Indy 500 winner Roger Ward and tuned by Vic Edelbrock Sr. The drag racers who experimented with the fuel in the early '50s, included Joaquin Arnett of Bean Bandits fame. The secret to power is hidden in nitromethane's chemical formula of CH3NO2. That O2 at the end is oxygen, which separates its chemical bonds to nitrogen during combustion and allows the oxygen to contribute to the combustion process. With gasoline, the air/fuel ratio for best power is 12.5 parts air to one part fuel (12.5:1). But because nitromethane contains its own oxygen, fuel racers long ago discovered that the more fuel you could feed the engine, the more power it made, bringing the air/fuel ratio closer to a 1:1 ratio.
Miller says if you compute the actual mechanical ratio of air and fuel with today's fuel engines, "the numbers get closer to 3 pounds of nitro for every 1 pound of air. But a lot of this fuel is used to cool the burn. People don't know this, but nitro, alcohol, and gasoline all have very similar burn rates," Miller says. "In fact, nitro is in between gasoline and methanol. All that lead [ignition timing] is due to the liquid fuel." In other words, the additional timing is necessary because, Miller says "only 10 percent of what's in the chamber is vapor; the rest is liquid." The vapor burns first, creating enough heat to begin to vaporize the rest of the liquid fuel. But this takes time, which means earlier ignition timing.
While some crewmembers wear gas masks during engine warm-up to avoid the fumes, improved p
Armstrong reinforced this concept. He says, "We used to have problems with head gaskets on our old Top Alcohol engines that never happened with the fuel engines. We realized that nitro burned slower. The horsepower doesn't really come from peak cylinder pressure. It actually drives the piston farther down the hole because it [the fuel] keeps burning." This longer burn is also why the header flames are so easy to see even during daylight. Armstrong also noted that this has an effect on cam timing. "You have to be careful when opening the exhaust valve. You can't open it too early-like before 82 to 84 degrees before bottom dead center (BDC) or it will just break parts. The cylinder pressure is so high that the valve just won't open. That's also why they keep the exhaust valve small, so it's easier to open."
This tremendous volume of fuel is what drives the requirement for the equally serious amount of ignition power required to light all this fuel. In an attempt to minimize engine damage, the NHRA has mandated a maximum of 90 percent nitromethane chased with 10 percent methanol. In case you're wondering, nitromethane does not mix well with gasoline, tending to separate into layers much like water and oil. However, there is a fuel called nitropropane (C3H7NO2) that does mix with gasoline. For the record, it tends to break pistons unless you know how to tune.
Top 10 Advancements in Top Fuel History
• Nitromethane fuel-first used successfully in circle track racing by Vic Edelbrock Sr.
• Marv Rifkin's design of the first flexible-sidewall M&H drag slick.
• The supercharger-first to be used were GMC diesel blowers.
• The Paul Schiefer slipper clutch along with Bruce Crower and the Crowerglide.
• The rear-engine chassis perfected by Don Garlits in 1971.
• The Dale Armstrong data logger through Racepak.
• Electric timers to engage lockup on clutches-Armstrong/Bernstein.
• Monster fuel pumps-Sid Waterman
• High-amperage magnetos.
• Parachutes for stopping-Simpson innovation.