The key to big power is optimizing the three pillars of internal combustion: fuel, air, and spark.
- For any internal combustion engine to function, you need three ingredients: fuel, air, and spark.
- All the motors competing in events sanctioned by the NHRA follow the same design as Chrysler’s original 500-cubic inch (8.1-liter) Hemi Elephant race engine from 1964.
- Drag racing is often unduly labelled as “boring” motorsport, but it’s actually quite the opposite if you understand what’s going on mechanically.
Like any self-respecting petrolhead, I’m captivated by all things internal combustion.
I’ve been to racetracks all over the world to see the best riders and drivers on two and four wheels, respectively. But few experiences are etched into my brain quite as deeply as when I heard two 11,000-horsepower Top Fuel dragsters fire off the starting line. Following such a visceral experience—which could’ve fooled me into thinking the world was ending—I did some digging to find out what makes these machines tick.
Drag racing is one of the simplest forms of motorsport; without any corners, pit stops, or gear changes, it boils down to “whoever’s fastest wins.” The sport began with a simple “run what you’ve brung” ethos, breeding big amounts of fun at little expense. However, the top level of the sport has since evolved into a horsepower shootout, with the fastest Top Fuel dragsters cranking out up to 11,000 hp.
For any internal combustion engine to function, you need three ingredients: fuel, air, and spark. These are the building blocks of horsepower. The engine in a Top Fuel dragster is largely similar to what you’ve got under the hood of your daily driver. The (frankly ridiculous) amount of power coming from these machines is made possible by optimizing that mixture of fuel, air, and spark.
Starting with fuel, these race cars use nitromethane instead of gasoline. This alternative “top fuel” (hence the name) is essentially gasoline that’s been pre-mixed with nitrous oxide. However, nitromethane is actually much less volatile than gasoline. Ergo, you can burn a lot more nitro in the combustion chamber, leading to much more power from every explosion inside the engine. Top Fuel dragsters are unsurprisingly thirsty machines, burning anywhere from 16 to 23 gallons of fuel throughout warmup, burnout, staging, and a four-second run.
This staggering fuel consumption not only makes big power, but also cools the engine. These dragster motors don’t have any cooling radiators. So how do they not instantly overheat? Another unique advantage of nitromethane is that it has an incredibly high latent heat of vaporization, which means it can absorb a massive amount of engine heat as it vaporizes. The sheer amount of fuel being injected into the combustion chamber allows for adequate cooling.
Through the course of each run, the spark plugs melt from the incredible amount of heat coming from the combustion chamber.
Top Fuel engines are actually quite simple in design. All the motors competing in events sanctioned by the NHRA follow the same design as Chrysler’s original 500-cubic inch (8.1-liter) Hemi Elephant race engine from 1964. The name “Hemi” came from the motor’s hemispherical (sphere-shaped) twin-valve combustion chambers. This design allowed for bigger valves, allowing much more air into the combustion chamber. And what does more air give you? More power.
While running a massive engine with equally large valves sounds like the perfect recipe for big power, it’s not enough when it comes to drag racing. This is where a supercharger (also referred to as a blower) forces even more air into the combustion chamber to produce more power. However, superchargers take power to make power; the blowers on Top Fuel dragsters generally need over 700 horsepower to provide the right amount of air for the car to produce the magic 11,000 hp. This is commonly referred to as parasitic loss.
Then we come to spark. Without sufficient spark, Top Fuel engines run the risk of hydro lock—where there’s more fuel in the combustion chamber than can be ignited—which can blow the cylinder head clean off the motor. This is the main reason why these motors use two spark plugs per cylinder, powered by twin magnetos that produce up to 44 amps of juice. However, through the course of each run, the spark plugs melt from the incredible amount of heat coming from the combustion chamber.
The spark plugs aren’t the only components being roasted inside the engine. During a race run, Top Fuel machines go through otherworldly levels of stress—so much that the pistons, rings, connecting rods, and spark plugs survive for only four seconds. To offer some perspective, most engines under the hood of road vehicles have a service interval of 3,000 hours.
Drag racing is often unduly labelled as “boring” motorsport, but it’s actually quite the opposite if you understand what’s going on mechanically. Any vehicle that can catapult itself up to over 300 miles per hour in the span of just over three seconds is a modern marvel.
From: Popular Mechanics
Matt Crisara Matt Crisara is a native Austinite who has an unbridled passion for cars and motorsports, both foreign and domestic, and as the Autos Editor for Popular Mechanics, he writes the majority of automotive coverage across digital and print.
Keyword: Here's How Top Fuel Dragsters Crank Out 11,000 Horsepower