Top Fuel


Top Fuel is a type of drag racing whose dragsters are the quickest accelerating racing cars in the world and the fastest sanctioned category of drag racing, with the fastest competitors reaching speeds of and finishing the runs in 3.641 seconds.
A top fuel dragster accelerates from a standstill to in as little as 0.8 seconds and can exceed in just. This subjects the driver to an average acceleration of about over the duration of the race and with a peak of over.
Because of the speeds, this class races a distance, not the traditional drag-race length of one-fourth of a statute mile, or. The rule was introduced in 2008 by the National Hot Rod Association after the fatal crash of Funny Car driver Scott Kalitta during a qualifying session at Old Bridge Township Raceway Park in Englishtown, New Jersey. The shortening of the distance was used by the FIA at some tracks, and as of 2012 is now the standard Top Fuel distance defined by the FIA. The International Hot Rod Association, which at the time sanctioned Top Fuel in Australia, dropped the 1/4-mile distance in September 2017 after a campaign by Santo Rapisarda, a car owner who often runs NHRA races in the United States.

Top Fuel racing

Before their run, racers often perform a burnout to clean and heat tires. The burnout also applies a layer of fresh rubber to the track surface, improving traction during launch.
At maximum throttle and RPM, the exhaust gases escaping from a dragster's open headers produce about of downforce. The massive airfoil over and behind the rear wheels produces much more, peaking at around when the car reaches about.
The engine of a Top Fuel dragster generates around 150 dB of sound at full throttle, enough to cause physical pain or even permanent damage. Before a run, race announcers usually advise spectators to cover or plug their ears. Ear plugs and even earmuffs are often handed out to fans at the entrance of a Top Fuel event.
Dragsters are limited to a wheelbase of.
The most prolific active driver in Top Fuel is Tony Schumacher and the most successful crew chief is Alan Johnson, who was the crew chief for six of Schumacher's championships, the back-to-back titles won by driver Gary Scelzi and was the crew chief for his brother Blaine for his entire professional career. The first female driver in the Top Fuel category is also the most associated female in the drag racing world, Shirley Muldowney, who won three championships during her career.

Fuel

Since 2015, NHRA regulations limit the composition of the fuel to a maximum of 90% nitromethane; the remainder is largely methanol. However, this mixture is not mandatory, and less nitromethane may be used if desired. While nitromethane has a much lower energy density than either gasoline or methanol, an engine burning nitromethane can produce up to 2.4 times as much power as an engine burning gasoline. This is made possible by the fact that, in addition to fuel, an engine needs oxygen in order to generate force: the stoichiometric ratio of petrol is 14.7:1 air to petrol, and 1.7:1 air to nitromethane, which, unlike gasoline, already has oxygen in its molecular composition. For a given amount of air consumed, this means that an engine can burn 7.6 times more nitromethane than gasoline.
Nitromethane also has a high latent heat of vaporization, meaning that it will absorb substantial engine heat as it vaporizes, providing an invaluable cooling mechanism. The laminar flame speed and combustion temperature are higher than gasoline's at and respectively. Power output can be increased by using very rich air-fuel mixtures. This also helps prevent pre-ignition, which is often a problem when using nitromethane.
Because of the relatively slow burn rate of nitromethane, very rich fuel mixtures are often not fully ignited, and some remaining nitromethane can escape from the exhaust pipe and ignite on contact with atmospheric oxygen, burning with a characteristic yellow flame. Additionally, after sufficient fuel has been combusted to consume all available oxygen, nitromethane can combust in the absence of atmospheric oxygen, producing hydrogen, which can often be seen burning from the exhaust pipes at night as a bright white flame. In a typical run the engine can consume between and of fuel during warmup, burnout, staging, and the quarter-mile run.

Top Fuel engines

Rules

Like many other motor sport formulas originating in the United States, NHRA-sanctioned drag racing favors heavy restrictions on engine configuration, sometimes to the detriment of technological development. In some cases, teams are required to use technologies that are decades old, resulting in cars that may seem substantially less advanced than the average family car. However, while some basic facets of engine configuration are heavily restricted, other technologies, such as fuel injection, clutch operation, ignition, and car materials and design, are under constant development.
NHRA competition rules limit the engine displacement to. A bore with a stroke are customary dimensions. Larger bores have been shown to weaken the cylinder block. Compression ratio is about 6.5:1, as is common on engines with overdriven Roots-type superchargers.

Engine

The engine used to power a Top Fuel drag racing car is based on a second generation Chrysler RB Hemi, but is built exclusively of specialized parts. It retains the basic configuration with two valves per cylinder activated by pushrods from a centrally-placed camshaft. The engine has hemispherical combustion chambers, a 58-degree intake to exhaust valve stem angle; bore pitch.
The block is machined from a piece of forged aluminum. It features press-fitted, ductile iron cylinder liners. There are no water passages in the block, which adds considerable strength and stiffness. The engine is cooled by the incoming air/fuel mixture and the lubricating oil. Like the original Hemi, the racing cylinder block has a deep skirt for strength. There are five main bearing caps, which are fastened with aircraft-standard-rated steel studs, with additional reinforcing main studs and side bolts. There are three approved suppliers of these custom blocks; Keith Black, Brad Anderson, and Alan Johnson.
The cylinder heads are machined from aluminum billets. As such, they, too, lack water jackets and rely entirely on the incoming air/fuel mixture and lubricating oil for their cooling. The original Chrysler design of two large valves per cylinder is used. The intake valve is made from solid titanium and the exhaust from solid Nimonic 80A or similar. Seats are of ductile iron. Beryllium-copper has been tried but its use is limited due to its toxicity. Valve sizes are around for the intake and for the exhaust. In the ports there are integral tubes for the push rods. The heads are sealed to the block by copper gaskets and stainless steel o-rings. Securing the heads to the block is done with aircraft-rated steel studs and stud nuts.
The camshaft is billet steel, made from 8620 carbon or S7 through-hardened tool steel or similar. It runs in five oil pressure lubricated bearing shells and is driven by gears in the front of the engine. Mechanical roller lifters ride atop the cam lobes and drive the steel push rods up into the steel rocker arms that actuate the valves. The rockers are of roller tip type on the intake and exhaust sides. Like the cam follower rollers, the steel tip roller rotates on a steel roller bearing and the steel rocker arms rotate on a pair of through-hardened tool steel shafts within bronze bushings. Intake and exhaust rockers are billet. The dual valve springs are of coaxial type and made out of titanium. Valve retainers are also made of titanium, as are the rocker covers.
Billet steel crankshafts are used; they all have a cross plane a.k.a. 90 degree configuration and run in five conventional bearing shells. 180 degree crankshafts have been tried. Due to ease of laying out an exhaust system with even pulsation, the 180 degree crankshaft can offer increased power in engines with interacting exhaust. However this does not concern Top Fuel engines with separate exhaust pipes for each cylinder. A 180 degree crankshaft is about lighter than 90 degree crankshaft, but they create a lot of vibration. Such is the strength of a top fuel crankshaft that in one incident, the entire engine block was split open and blown off the car during an engine failure, and the crank, with all eight connecting rods and pistons, was left still bolted to the clutch.
Pistons are made of forged aluminum. They have three rings and aluminum buttons retain the steel wrist pin. The piston is anodized and Teflon coated to prevent galling during the high thrust load operation encountered. The top ring is an L-shaped section "Dykes" ring that provides the best seal during combustion, but a second ring must be used to prevent excessive oil from entering the combustion chamber during intake strokes, as the Dykes-style ring offers less than optimal reverse gas/oil sealing. The third ring is an oil scraper ring whose function is to scrape the majority of the oil film off the cylinder wall as the piston descends from top dead center, to prevent oil being exposed to combustion heat and contaminating the upcoming round of fuel/air. This "oil scraping" also provides a key heat removal step for the cylinder walls and piston skirts; the oil film is renewed as the piston moves upward after reaching bottom dead center.
The connecting rods are of forged aluminum and do provide some shock damping, which is why aluminum is used in place of titanium, endangering the bearings and thus the crankshaft and block. Each con rod has two bolts, shell bearings for the big end while the pin runs directly in the rod.

Superchargers

The supercharger must be a 14-71 type Roots blower. It has twisted lobes and is driven by a toothed belt. The supercharger is slightly offset to the rear to provide an even distribution of air. Absolute manifold pressure is usually, but up to is possible. The manifold is fitted with a burst plate. Air is fed to the compressor from throttle butterflies with a maximum area of. At maximum pressure, it takes approximately to drive the supercharger.
These superchargers are in fact derivatives of General Motors scavenging-air blowers for their two-stroke diesel engines, which were adapted for automotive use in the early days of the sport. The model name of these superchargers delineates their size - the once commonly used 6-71 and 4-71 blowers were designed for General Motors diesels having six cylinders of each, and four cylinders of each, respectively. Thus, the currently used 14-71 design can be seen to be a huge increase in power delivery over the early designs, purpose-built for the GM Detroit Diesel truck powerplants.
Mandatory safety rules require a secured Kevlar-style blanket over the supercharger assembly as "blower explosions" are not uncommon, from the volatile air/fuel mixture coming from the fuel injectors being drawn directly through them. The absence of a protective blanket exposes the driver, team and spectators to shrapnel in the event that nearly any irregularity in the induction of the air/fuel mixture, the conversion of combustion into rotating crankshaft movements, or in the exhausting of spent gasses is encountered.