How a Top Fuel Dragster Works

The basics of drag racing are indeed rather elementary. Everyone lines up and goes on the same signal, accelerating to a spot some distance away on a straight course, and whoever gets there first wins. That's consistent across all four National Hot Rod Association (NHRA) Mello Yello drag racing series: Top Fuel, Funny Car, Pro Stock and Pro Stock Motorcycle. The starting light, popularly known as the Christmas tree, flashes a series of amber lights to let the drivers get ready. At the end, there's a green light to go, but if anyone takes off too early, that's a foul and that also gets a red light. The distance varies depending on the specific series. Top Fuel cars and Funny Cars sprint to a distance of 1,000 feet (304.8 meters) to determine the victor.

There's a lot more to a race than just watching it, though. The National Hot Rod Association (NHRA)divides its race cars into categories, based on criteria such as engine type, the car's weight, acceptable modifications to the car, aerodynamics and fuel type. The fuel type is primarily what we'll be focusing on, since it's the main factor that differentiates Top Fuel dragsters. They're some of the fastest vehicles on the planet. In fact, just one of the eight cylinders in a Top Fuel engine makes as much horsepower as a NASCAR Sprint Cup car [source: McGee]. But Funny Cars are mechanically similar to Top Fuel cars, so to some extent, it's worth taking a look at both types.

Top Fuel cars get their power from custom engines that are 500 cubic inches and boast superchargers, making them capable of around 8,000-horsepower. Though some estimates go as high as 10,000-horsepower -- and there's a good reason for any discrepancies [source: Mazlumian]. Top Fuel engines can't be measured by a dynamometer, the machine that evaluates a car's horsepower and torque. So, Top Fuel power numbers are calculated by mathematical equations, which can leave some room for debate. These engines can't burn regular gasoline, or even race gas. They need nitromethane, a special kind of fuel, which is how these cars got the Top Fuel name. Their super powerful engines have to be fed with much more concentrated power, which is no accident. It's a complicated balance, requiring the cars to be tuned specifically for the fuel, and the fuel to be manufactured specifically for the cars. All the effort is worth it to the racers, who travel at previously unheard-of speeds, and the fans, who love the flames that occasionally blast from Top Fuel dragsters' tailpipes.

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. Somehow, though, Germans in the 1930s and Americans in the 1940s independently discovered that nitromethane could also power race cars. Sometimes, they were victorious; other times, the results were disastrous, since the fuel is so dangerous to work with. But they kept on, and those experiments over the decades helped develop the Top Fuel cars we have today.

Nitromethane is particularly volatile, especially since it doesn't need to mix with air to combust. 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. It can also reportedly explode upon almost any kind of impact [source: Davis]. This is one of the explanations for the flames that come from the exhaust pipes -- unburned fuel heats up as it exits through the exhaust system and ignites when it comes into contact with the atmosphere.

An engine that runs on nitromethane is typically of much lower compression than a gasoline engine (which seems counterintuitive), because lower compression engines generally need less powerful fuel [source: Davis]. Unlike gasoline, though, nitromethane carries oxygen, so the engine doesn't need to force in as much air for the combustion cycle that makes power, allowing it to run at lower compression. This is just one of the finicky tolerances that a Top Fuel mechanic needs to watch carefully so the car remains stable under load. The engines and components are under so much pressure that 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].

Currently, Top Fuel and Funny Cars 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; but 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.

Race Day!

Even though whoever gets to the finish line first is crowned the victor of an NHRA drag race, that doesn't mean the winning car is necessarily the fastest. It also doesn't mean that car is the quickest. If a car is the first off the line, that's a huge advantage in a race that only covers a short distance. Even if the other car has a faster top-speed, it might not be able to cover the lost ground to take the win. So, even though the races are brief, there's always a lot of action.

Top Fuel cars take off from the starting line and reach a speed of 100 miles per hour (160.9 kilometers per hour) in less than a second. This makes them the fastest accelerating machines in the world. (Not just the fastest cars to accelerate, but the fastest anything to accelerate.) The engine's power reaches the wheels in a lickety-split fraction of a second -- 15/100, to be precise. At launch, Top Fuel drivers endure G-forces similar to astronauts during a space shuttle launch. And almost just as quickly, they need to stop. Since these cars would wear through brakes pretty quickly at more than 300 miles per hour (482.8 kilometers per hour), Top Fuel dragsters are equipped with a special type of primary braking system. After crossing the finish line, the driver hits a switch that deploys two parachutes behind the car, and the intense wind resistance slows the car with little risk of additional mechanical failure.

Funny Cars use the same kind of engines as Top Fuel cars, but there are plenty of differences. The first Funny Cars were 1960s HEMI-powered Dodge models, and they didn't become part of the NHRA until around 1969. The rear wheel placement has been slightly adjusted, and the rear tires are a lot larger now, too. The different wheelbase of Funny Cars, as compared to Top Fuel cars, may account for some of the differences in speed and acceleration, since the huge amount of power going to the rear wheels can cause a lot of extra movement as the cars zip down the strip. In Top Fuel cars, the engine is situated behind the driver, but Funny Cars put the engine up front. Funny Cars use the wheelbase of a production car from the model year 2000 or later, and then a fiberglass replica of the body is constructed to reduce weight. The rules for using production cars offer a lot of leeway. Racers can use sports cars, coupes, or sedans from any domestic or import auto manufacturer, as long as the car was originally mass produced. In other words, race teams can't modify concept cars or show cars or hand-built boutique cars. To be eligible under the NHRA's rules, the car must have been built on a factory assembly line. At one point, about 20 years or so ago, there was talk of changing the Funny Cars' official name to "Fuel Coupe" and the similar names may have strengthened the connection between Top Fuel and Funny Cars -- at least in fans' minds [source:Klinger].

Top Fuel drag cars and Funny Cars have similar performance specs, thanks to the related mechanical components. Over the 1,000-foot (304.8-meter) straightaway, these dragsters reach speeds above 300 miles per hour (482.8 kilometers per hour) and complete the distance in three to four seconds, burning about 1.2 gallons (4.54 liters) of nitromethane blend per second, and about 17 gallons (64.35 liters) per race [source: Mazlumian]. Another way to get a sense of these cars' capabilities is to look at the records. At the start of the 2014 season, the record for fastest Top Fuel car in the series was 332.18 miles per hour (534.6 kilometers per hour), held by Spencer Massey, and for the Funny Car series, the top-speed recorded was Matt Hagan's 320.66 miles per hour (516.1 kilometers per hour). Antron Brown's car completed a Top Fuel run in just 3.701 seconds, and Jack Beckman's Funny Car record is 3.986 seconds.

Don't Forget Your Earplugs

Motorsports fans are advised to wear some kind of ear protection when they're watching Top Fuel racing live. Easily obtainable foam earplugs, like the kind that you'd wear to catch some sleep on a long plane trip, can cut the sound by about 20 decibels [source: McGee]. That's not a lot, as you'll see, but it's better than nothing. Hearing damage is usually permanent, and once it starts, it's irreversible. And Top Fuel dragsters are the worst noise offenders out there.

Top Fuel dragsters are the NHRA's loudest cars, in part because of the way the engine is mounted. If it was under a hood like a normal car, there'd be at least some insulation to muffle the sound; however, it's completely exposed, and all the engine's workings are right out there -- oh, and there are no mufflers either. The NHRA once allowed a team of seismologists to stand at the starting line to measure the race the way they would measure an earthquake -- the two cars rated a 2.3 on the Richter scale [source: McGee]. That's equivalent to a minor quake, the kind that might go overlooked by some people in the vicinity, but others will definitely feel it. So, the Top Fuel cars' rankings on the earthquake scale are somewhat low, but the fact remains that these are cars that were once officially and scientifically compared to earthquakes. And that's about the most official research that's ever been done. According to ESPN, even though the NHRA will let seismologists take meter readings, they've never recorded official noise levels, and it's unlikely they ever will. It's all part of the mystique surrounding the sport, they explain. That, and once there are official decibel levels on-record, there's a lot more grounds for complaint and protest. In 2010, an ESPN reporter scrambled around to find a sound meter capable of testing a Top Fuel drag run -- the highest he could record was 140 decibels, with the meter blinking to indicate its capacity was topped out. Experts estimate Top Fuel cars can reach over 150 decibels, a level that can cause physical damage to the eardrum. For comparison's sake, a typical rock-concert is about 104 to 120 decibels.

There's no sign of Top Fuel popularity slowing down anytime soon. In fact, over just the last few years, the cars themselves have become even more powerful. And the faster a Top Fuel car goes, the louder it gets, which means that as technology continues to improve, more and more drivers are encountering hearing loss [source:McGee]. Fans will have to deal with more potential hearing damage, too. It's just one of the many well-publicized risks of racing, but for the drivers and the fans, the smell of burning nitromethane is well worth it.