Top Fuel

Because of the speeds involved, Top Fuel races a 1,000-foot (304.8 m) distance rather than the traditional quarter-mile (1,320 feet / 402.3 m). The National Hot Rod Association introduced the shorter distance in 2008 following the fatal crash of Funny Car driver Scott Kalitta during a qualifying session at Old Bridge Township Raceway Park in Englishtown, New Jersey. The FIA adopted the 1,000-foot standard at some tracks and formalised it as its global Top Fuel distance in 2012. The International Hot Rod Association, which at the time sanctioned Top Fuel in Australia, dropped the quarter-mile distance in September 2017 following a campaign by car owner Santo Rapisarda.

Before a run, racers perform a burnout to clean and heat the tyres and apply a fresh layer of rubber to the track surface. At maximum throttle and RPM, exhaust gases from a dragster's open headers produce approximately 900–1,100 pounds-force (4.0–4.9 kN) of downforce. The massive airfoil over the rear wheels produces considerably more, peaking at around 12,000 pounds-force (53.4 kN) when the car reaches approximately 330 mph (531.1 km/h). Dragsters are limited to a wheelbase of 300 inches (7.6 m).

At full throttle, a Top Fuel engine generates around 150 dB of sound — enough to cause physical pain or permanent hearing damage. Race announcers typically advise spectators to cover or plug their ears before a run, and ear plugs and earmuffs are often distributed at the entrance to Top Fuel events.

Since 2015, NHRA regulations limit fuel composition to a maximum of 90% nitromethane, with the remainder largely methanol. Nitromethane has a much lower energy density (11.2 MJ/kg) than gasoline (44 MJ/kg) or methanol (22.7 MJ/kg), but an engine burning nitromethane can produce up to 2.4 times as much power as one burning gasoline. This is possible because nitromethane carries oxygen in its molecular composition: the stoichiometric ratio is 1.7:1 air to nitromethane compared to 14.7:1 air to petrol, meaning an engine can burn 7.6 times more nitromethane than gasoline for a given amount of air consumed.

Nitromethane has a high latent heat of vaporisation, absorbing substantial engine heat as it vaporises. Its laminar flame speed and combustion temperature are higher than gasoline's — 0.5 m/s (1.6 ft/s) and 2,400 °C (4,350 °F) respectively. Because of nitromethane's relatively slow burn rate, unburned fuel often escapes from the exhaust and ignites on contact with atmospheric oxygen, producing a characteristic yellow flame. After all available oxygen has been consumed, nitromethane can combust without atmospheric oxygen to produce hydrogen, visible as a bright white flame from the exhaust pipes at night. In a typical run the engine consumes between 12 US gallons (45.42 L) and 22.75 US gallons (86.12 L) of fuel during warm-up, burnout, staging, and the run itself.

NHRA competition rules limit engine displacement to 500 cubic inches (8.19 L). The standard bore is 4.1875 inches (106.36 mm) with a 4.5-inch (114.30 mm) stroke. Compression ratio is approximately 6.5:1, as is common on engines with overdriven Roots-type superchargers.

The engine used in a Top Fuel dragster is based on a second-generation Chrysler RB Hemi but is built exclusively from specialised parts. It retains the basic configuration of two valves per cylinder activated by pushrods from a centrally-placed camshaft, with hemispherical combustion chambers, a 58-degree intake-to-exhaust valve stem angle, and a 4.8-inch (121.92 mm) bore pitch. There are three approved suppliers of the custom aluminium block: Keith Black, Brad Anderson, and Alan Johnson.

The cylinder heads are machined from aluminium billets and lack water jackets, relying on the incoming air/fuel mixture and lubricating oil for cooling. Intake valves are solid titanium; exhaust valves are Nimonic 80A or similar. Valve sizes are approximately 2.45 in (62.23 mm) for intake and 1.925 in (48.90 mm) for exhaust.

The supercharger must be a 14-71 type Roots blower with twisted lobes, driven by a toothed belt. Absolute manifold pressure is usually 56–66 psi (386–455 kPa). At maximum pressure it takes approximately 1,000 horsepower (750 kW) to drive the supercharger. These blowers are derivatives of General Motors scavenging-air blowers originally designed for two-stroke diesel engines; the 14-71 designation indicates a design scaled from the 6-71 and 4-71 units built for GM Detroit Diesel truck powerplants. A secured Kevlar-style blanket over the supercharger assembly is mandatory, as blower explosions are not uncommon from the volatile air/fuel mixture being drawn directly through them.

Fuel is delivered by a constant-flow injection system with approximately 42 nozzles. The engine-driven mechanical fuel pump can flow 100 US gallons (380 L) per minute at 7,500 rpm and 500 psi (3,450 kPa) fuel pressure.

The exhaust system consists of eight individual open pipes — called "zoomies" — 2.75 in (69.85 mm) in diameter and 18 in (457.20 mm) long, directing exhaust upward and backward. Exhaust temperature is approximately 500 °F (260 °C) at idle and 1,796 °F (980 °C) at the end of a run.

Calculated power output is estimated between 8,500 and 10,000 hp (6,340–7,460 kW). In late 2015, tests using sensors developed by AVL Racing showed peak power of over 11,000 hp (8,200 kW). A Top Fuel engine cannot be run at maximum power for more than 10 seconds without potentially destroying itself; after each run the entire engine is disassembled, inspected, and worn or damaged components are replaced.

Much of organised drag racing is sanctioned by the NHRA, which has held regional and national events since 1955. Contemporary Top Fuel safety equipment includes full-face helmets with HANS devices, multi-point quick-release harnesses, full Nomex body suits, on-board fire extinguishers, Kevlar blankets around the supercharger and clutch assemblies, damage-resistant fuel tanks and lines, externally accessible fuel and ignition shut-offs, and braking parachutes.

In 2000, the NHRA mandated a maximum nitromethane concentration of 90%. Following a fatality at Gateway International Raceway in 2004 involving racer Darrell Russell, the limit was temporarily reduced to 85%, but complaints from teams about mechanical failures caused by the leaner mixture led to its restoration to 90% in 2008. The NHRA also mandated enclosed roll cages and different rear tyres following the Gateway fatality. Rear tyre pressure is regulated by Goodyear Tire and Rubber on behalf of the NHRA at 7 psi (48 kPa). Final drive ratios higher than 3.20 are prohibited to limit top-speed potential.

In 2012, the NHRA allowed enclosed cockpits to be used regularly in Top Fuel competition.

In 1958, the NHRA banned nitromethane in all categories. The American Hot Rod Association (AHRA) still permitted it, and independent drag strips not sanctioned by the NHRA provided venues for fuel racers. The Smokers Car Club hosted the first U.S. Fuel and Gas Championship at Famoso Raceway in March 1959, with Bob Hansen winning Top Fuel Eliminator in his A/HR at a speed of 136 mph (218.9 km/h).

Don Garlits introduced the Swamp Rat XIV — a rear-engined Top Fuel dragster — in 1971. While earlier rear-engined designs had been attempted in the previous decade, the Swamp Rat XIV was the first successful one, winning the 1971 NHRA Winternationals.

In 1984 Top Fuel was at a low point, having trouble attracting full sixteen-car fields, which led to fields being cut to eight cars while the International Hot Rod Association dropped Top Fuel entirely. The same year, Joe Hrudka offered a major purse through the Cragar-Weld Top Fuel Classic and Don Garlits returned to Top Fuel full-time. By 1987, NHRA Top Fuel Funny Car was drawing twice as many entrants as positions available.

The most prolific active driver in Top Fuel is Tony Schumacher. The most successful crew chief is Alan Johnson, who served as crew chief for six of Schumacher's championships, for the back-to-back titles won by driver Gary Scelzi, and for his brother Blaine throughout his entire professional career. Shirley Muldowney was the first female driver in the Top Fuel category and won three championships during her career.

This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.