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'Top-Fuel Racing' refers to a class of drag racing in which the cars are run on a maximum of 85% nitromethane and about 15% methanol (also known as racing alcohol), instead of gasoline. The cars are purpose built race cars, with a layout superficially resembling open-wheel circuit racing vehicles - however, they are much longer, much narrower, and have very thin front tyres, to optimize their performance exclusively in a straight line.
Like other drag racing classes, these cars compete in a 1/4 mile (0.4 km) race. They are the fastest such category, with the fastest cars completing it in less than 4.5 seconds at upwards of 330 mph (530 km/h). A Top Fuel dragster accelerates from 0 to 100 mph (160 km/h) in less than 0.8 second, subjecting the driver to a force about 5.7 times his weight. This acceleration takes less than a tenth of the time needed by a production Porsche 911 Turbo to reach the same speed. A fuel dragster can exceed 280 mph (450 km/h) in just 660 feet (0.2 km). For further information and standards for drag-racing, including safety requirements, see NHRA.

Contents

Facts about Top Fuel

The Fuel

Top fuel engines

Performance

Engine weight

Anatomy of a Top Fuel Dragster

Mandatory safety equipment

References

External links

Facts about Top Fuel

Before their run, they do a ''burnout''. This is done for three reasons. First, after applying some water, it heats the tires up, which results in better traction. Secondly, it removes debris from the tires. Thirdly, and most importantly, it coats the track surface with rubber which greatly improves traction during the subsequent launch. A top fuel dragster's burnout alone can travel one quarter of the way down the track.
At top engine speed, the exhaust gases escaping from the open headers produce about 800-1000 pounds-force (3.6 kilonewtons) of downforce. The massive foil over and behind the rear wheels produces much more downforce, peaking at around 12,000 lb_f when the car reaches a speed of about 325 mph.
Top Fuel dragsters are notorious for the deafening amount of noise their engines create-at full throttle. They generate over 150 dB, enough to cause some peoples' eardrums physical pain. The intense levels of sound are not only heard, but also felt as pounding vibrations all over one's body, leading many to compare the experience of watching a Top Fuel dragster make a pass to 'feeling as though the entire drag strip is being bombed'. Prior to the dragsters going down the strip, race announcers usually advise spectators to cover or plug their ears—indeed, ear plugs and even earmuffs are often handed out to fans at the entrance to a Top Fuel event.

The Fuel

NHRA regulations limit the composition of the fuel to a maximum of 85% nitromethane; the remainder is largely methanol. However, this mixture is not mandatory, and less nitromethane can be used if desired.
Kenny Bernstein was the first drag racer in NHRA history to break 300 mph in the 1/4 mile in March, 1992. Kenny took his digger (slang for dragster) over 300 mph using a mixture of 90-to-100% nitromethane at the time. Despite nitromethane having a much a lower energy density (11.2 MJ/kg) than either gasoline (44 MJ/kg) or methanol (22.7 MJ/kg), its addition to the fuel mixture has the net effect of increasing engine output by around 2.3 times compared to gasoline for the same mass of air.
The high temperature of vaporization of nitromethane also means that it will absorb substantial engine heat as it vaporizes, providing an invaluable cooling mechanism. Compared to gasoline the laminar flame speed and combustion temperature are higher at 0.5 m/s and 2400°C respectively. Power output can be increased by using very rich air fuel mixtures. This is also something that helps prevent detonation, something that is usually a problem when using nitromethane.
Due to 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 as much as 103 litres (22.75 gallons) of fuel during warmup, burnout, staging, and the quarter-mile run.

Top fuel engines

Like many other motor sport formulas originating in the United States, the NHRA favors heavy restrictions on engine configuration, rather than technological development. This restricts the teams to using many decades old technologies.
The engine used to power a Top Fuel drag racing car has its roots in the second generation Chrysler Hemi 426 "Elephant Engine" made 1964-71. Although the Top Fuel engine is built exclusively of aftermarket 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 90 degree V angle; 4.8" bore pitch and a 5.4" camshaft height. The configuration is identical to the overhead valve, single camshaft-in-block "Hemi" V-8 engine which became available for sale to the public in selected Chrysler Corporation (Dodge, DeSoto, and Chrysler) automotive products in 1952.
The NHRA competition rules limit the displacement to 500 cubic inch (8193.5 cc). A 4.19" (106.4 mm) bore with a 4.5" (114.3 mm) 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 (the supercharger is driven faster than the crankshaft speed) superchargers.
The block is CNC machined from a piece of forged aluminium. It has press-fitted ductile iron liners. There are no water passages in the block which adds considerable strength and stiffness. Like the original Hemi, the racing cylinder block has a long skirt (to reduce piston "rocking" at the lower limit of piston travel); 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-made after-market blocks, from which the teams may choose.
The cylinder heads are CNC-machined from aluminum billets. As such, they have no water jackets and rely entirely on the incoming air/fuel mixture 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 have been tried but its use is limited due to cost. Valve sizes are around 2.45" (62.2 mm) for the intake and 1.925" (48.9 mm) 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 bolts.
The camshaft is billet steel, made from 8620 carbon 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 rockers that actuate the valves. The rockers are of roller type on the intake side, high pressures on the exhaust limits its use to the intake side only. The steel roller rotates on a steel roller bearing and the steel rocker arms rotates on a titanium shaft within bronze bushings. Intake rockers are billet while the exhausts are investment cast. 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 runs in five conventional bearing shells. 180 degree crankshafts have been tried and they can offer increased power, even though the exhaust is of open type. A 180 degree crankshaft is also about 10 kg 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 of forged aluminium, 2618 alloy. They have three rings and aluminium buttons retain the 1.156" x 3.300" steel pin. The piston is anodized and Teflon coated to prevent galling during high temperature operation. The top ring is an L-shaped Dykes ring that provides a good seal during combustion but a second ring must be used to prevent oil from entering the combustion chamber during intake strokes as the Dykes-style ring offers less than optimal combustion gas sealing. The third ring is an oil scraper ring whose function is helped by the second ring.
The connecting rods are of forged aluminium and do provide some shock damping, which is why aluminum is used in place of titanium, because titanium connecting rods transmit too much of the combustion impulse to the big-end rod bearings, 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.
The supercharger is 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 3.8-4.5 bar (56-66 PSI), but up to 5.0 bar (74 PSI) is possible. The manifold is fitted with a 200 psi burst plate. Air is fed to the compressor from throttle butterflies with a maximum area of 65 sq. in. 45.5 Maximum boost, in PSI, produced by the supercharger at wide-open throttle.
These superchargers are in fact derivatives of General Motors scavenging-air blowers for their two-cycle diesel engines, which were adapted for automotive use in the early days of the sport. The model name of these superchargers delineates their size; ''i.e.'' the once commonly used 6-71 and 4-71 blowers were designed for General Motors diesels having six cylinders of 71 cubic inches each, and four cylinders of 71 cubic inches each, respectively. Thus, the currently used 14-71 design can be seen to be a huge increase in power delivery over the early designs.
Mandatory safety rules require a secured Kevlar-style blanket over the supercharger assembly as "blower explosions" are not uncommon. 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.
The oil system has a wet sump which contains 16 quarts of SAE 70 mineral or synthetic racing oil. The pan is made of titanium or aluminium. Titanium can be used to prevent oil spills in the event of a blown rod. Oil pressure is somewhere around 160/170 lb during the run, 200 lb at start up, but actual figures differs between teams.
Fuel is injected by a constant flow injection system. There is an engine driven mechanical fuel pump and about 42 fuel nozzles. The pump can flow 100 gallons/minute at 8000 rpm and 500 PSI fuel pressure. In general 10 injectors are placed in the injector hat above the supercharger, 16 in the intake manifold and two per cylinder in the cylinder head. Usually a race is started with a leaner mixture, then as the clutch begins to tighten as the engine speed builds, the air/fuel mixture is enriched. As engine speed builds pump pressure the mixture is made leaner to maintain a predetermined ratio that is based on many factors, one of which is primary one of race track surface friction. The stoichiometry of both methanol and nitromethane is considerably greater than that of racing gasoline, as they have oxygen atoms attached to their carbon chains and gasoline does not. This means that a "fueler" engine will provide power over a very broad range from very lean to very rich mixtures. Thus, to attain maximum performance, before each race, by varying the level of fuel supplied to the engine, the mechanical crew may select power outputs barely below the limits of tire traction. Power outputs which create tire slippage will "smoke the tires" and the race is often lost.
The air/fuel mixture is ignited by two 14 mm spark plugs per cylinder. These plugs are fired by two 44-amp magnetos. Normal ignition timing is 58-65 degrees BTDC. (This is dramatically greater spark advance than in a gasoline engine as "nitro" and alcohol burn far slower.) Directly after launch the timing is typically decreased by about 25 degrees for a short time as this gives the tires time to reach their correct shape. The ignition system limits the engine speed to 8400 rpm. The ignition system provides initial 50,000 volts and 1.2 amps. The long duration spark (up to 26 degrees) provides energy of 950 millijoules. The plugs are placed in such a way that they are cooled by the incoming charge. The ignition system is not allowed to respond to real time information (no computer-based spark lead adjustments), so instead a timer-based retard system is used.
The engine is fitted with open exhaust pipes, 2.75" in diameter and 18" long. These are made of steel and fitted with thermocouples for measuring of the exhaust temperature. They are called "zoomies" and exhaust gases are directed upward and backwards. Exhaust temperature is about 260 °C at idle and 980 °C by the end of a run. A night run provides visual excitement with slow-burning nitromethane flames many feet above this screaming spectacle of acceleration. A "good run" is over in just 4.5 seconds, the noise ends, and braking parachutes are seen in the distance, after a speed of over 325 miles per hour has been reached.
The engine is warmed up for about 80 seconds. After the warm up the valve covers are taken off, oil is changed and the car is refueled. The run including tire warming is about 100 seconds which results in a "lap" of about three minutes. After each lap, the whole engine is taken apart and gone through, and much of it is replaced.

Performance

Power output of these engines is most likely somewhere between 7000 and 8300 horsepower (approximately 4500-6000 kilowatts). It is often inexplicably stated that no dynamometer exists that can measure the output of a Top Fuel Engine. Dynamometers capable of measuring tens of thousands of horsepower at relevant shaft speeds are in widespread use. Estimates suggest a torque output of 5100-6750 Nm (3760-4980 lb-ft) and also a brake mean effective pressure of 80-100 bar.
For the purposes of comparison, a 2007 Bugatti Veyron, one of the world's fastest production vehicles, produces ~1,000 horsepower.

Engine weight

★ Block with liners 85 kg

★ Heads 18 kg each

★ Crankshaft 37 kg

★ Complete engine 225 kg.

Anatomy of a Top Fuel Dragster

'Specifications'
According to 2004 FIA regulations, a Top Fuel dragster must weigh no less than 2175 pounds (989kgs) after the run including the driver. The wheelbase must not exceed 300 inches (7.62 meters). From the front of the car to a point 12 inches (30.5cm) behind the center line of the front axle the car must maintain a minimum ground clearance of 3 inches (7.6cm). The top of the rear wing may not be higher than 90 inches (230cm) from ground level. The front overhang of the nose may not exceed 30 inches (76cm), measured from the center line of the front axle.
'Data Logger'
There are no computer controlled functions on the car at all but crews can log data such as exhaust temperatures, fuel pressure, fuel flow, crank shaft speed, rear axle speed and supercharger pressure to maximise the cars potential and help tune the cars performance on the next run. The cost is around £12,000.

'1. Wings'
An integral part of keeping a 7000bhp Top Fuel Dragster on the track at over 300mph in a time of just over 4.6 seconds is the massive rear wing and the front canard wings. The latest exert a down force of some 8000lpb for the rear and 1800lpbs for the front helping to adhere the vehicle to the track. Wing elements can be adjusted to different angles depending on the track conditions, atmospheric pressure and how the car is setup. The cost of a rear wing is approximately £5,000 with the front being around £1,500.
'2. Engine'
The engine is loosely based on the famed 426 cubic inch Chrysler Hemi with a maximum displacement of 500c.i. with the billet aluminium block being supplied by several US manufacturers costing around £4,000 each. An engine that comes compete with billet aluminium heads, intake manifold, supercharger, fuel pump, magneto's and is ready to go costs approximately £60,000.
'3. Supercharger'
Sitting on top of the motor intake manifold is a mechanical belt driven device that literally rams air at a colossal rate into the engine. A typical supercharger turning at 11,000rpm will displace 110,000 cubic inches of air per minute.
'4. Driver Safety Equipment'
A complete multi layer fire resistant driving suit and gloves must be worn, together with state of the art crash helmet with fire resistant lining and neck cut off. Because of the G-forces exerted on the driver, the helmet is linked into the safety harness via a chinstrap. For the same reason a 360-degree neck collar and a Hans device is also worn to protect from whiplash should a high-speed crash occur. Drivers are secured in the cockpit with a five-point restraint system utilising a safety harness with 3 inch wide lap and shoulder belts which are covered with the fire resistant material. Arm restraints keep the arms inside the cockpit in the event of a roll over.
'5. Body'
A multiple piece body formed of magnesium alloy and carbon fiber is attached to the chassis with quick release fasteners, commonly referred to as Dzus fasteners. The nose, rear wing, front wing assembly, kick outs and cockpit cover are usually all carbon fibre.
'6. Tyres'
The Goodyear slicks on the back are 18.5 inches (47cm) wide and nearly 9.5 feet (3 meters) in circumference. Dependant upon track and atmospheric conditions, rear tyre pressure is between 6.5 and 7 pounds per square inch. Front tyres are 2.5 inches (6.25cm) wide and 22 inches (56cm) in diameter and are between 70 and 100psi.
'7. Rolling Chassis'
A Top Fuel chassis is fabricated from 300 feet of 4130 chrome moly tubing and costs approximately £40,000 complete.
'8. Fuel System'
Delivery of fuel to the engine is controlled by a pneumatically timed enrichment system, which runs in a parallel to the clutch control and ignitions systems. The volume of fuel increases in the line with the increase of clutch pressure to keep the fuel to air ratio correct for the amount of power that the engine needs to produce at any given point during the run. Put simply the engine does not need the same amount of fuel on the start line as it does 3 seconds onto the run. The power elixir that helps coax more than 13 horsepower from each of the engines 500 cubic inches is the fuel - nitromethane. Nitromethane is produced by the nitration of propane; the end result is CH3NO2. A maximum of 90% nitromethane is allowed under the rules with the other 10% being methanol. The mix can be less than 90% depending upon atmospheric conditions. Nitro is fed to the engine by a single four gear fuel pump that delivers between 85 and 100 US gallons (approx. 300 litres) per minute dependant on the crew chiefs set up. During warm up, burn out procedure and a quarter mile run, a typical Top Fueller will gulp 15 gallons (56 litres) of nitro costing around £35 per litre!
'9. Ignition'
The big advance in performance in recent years has been due to more efficient magnetos. Modern magnetos are so powerful they have allowed greater amounts of fuel to be burnt efficiently, therefore increasing the power output of the engine. Coupled with this is the multiple advance and retard systems now available that allow the Crew Chief to change the timing of the ignition spark, either increasing or reducing power, to give optimum traction. The cost of these systems is approximately £10,000.
'10. Drivetrain'
To prevent a loss of traction, power is transferred from the engine to the rear tyres via a complex timer controlled hydro-pneumatic clutch system. Centrifugal force on the clutch arms creates pressure on the five discs and four steel floater plates. The pressure is increased gradually in a series of minute stages. This involves a hydraulic ram, the speed of movement of which is controlled by a series of timed adjustable restrictors. The clutch will slip for approximately 3 seconds into the run until complete lock up with the engine and drive chain is achieved. This is not a computer-controlled function but is pre set before the run. Typically clutch temperatures can reach in excess of 1,000 degrees Fahrenheit. All Top Fuel cars run a standard rear gear ratio of 3.20:1.
'11. Brakes'
The rear brake rotors measure approximately 11 inches (28cm) in diameter and are made from carbon fiber, activated via a hand lever in the cockpit and utilized only on the rear axle. The car's primary braking system is a pair of parachutes that can produce up to 6 negative G forces of stopping power. A direct opposite to the G forces felt by the driver at launch.

Mandatory safety equipment

Much of organized drag-racing is sanctioned by the National Hot Rod Association. Since 1955, the Association has held regional and national events (typically organized as single elimination tournaments, with the winner of each two car race advancing) and has set rules for safety, with the more powerful cars requiring ever more safety equipment.
Typical safety equipment for contemporary top fuel dragsters: full face helmets with fitted HANS devices; multi-point, quick release safety restraint harness; full body fire suit made of Nomex or similar material, complete with face mask, gloves, socks and shoes, all made of fire-resistant materials; on board fire extinguishers; kevlar or other synthetic "bullet-proof" blankets around the superchargers and clutch assemblies to contain broken parts in the event of failure or explosion; damage resistant fuel tank, lines, and fittings; externally accessible fuel and ignition shut-offs (built to be accessible to rescue staff); braking parachutes; and a host of other equipment, all built to the very highest standards of manufacturing. Any breakthrough or invention that is likely to contribute to driver, staff, and spectator safety is likely to be adopted as a mandated rule for competition. The forty year history of NHRA has provided hundreds of examples of safety upgrades.
In 2000, the NHRA mandated the maximum concentration of nitromethane in a car's fuel be no more than 90%. Following an incident at a national event in 2004 in Madison, IL in which Top Fuel driver Darrell Russell was killed, the NHRA cut the fuel ratio to the present 85%. The NHRA also mandated that different rear tires be used (in both Top Fuel and Funny Car) to try to prevent them from failing and that a titanium "shield" be attached around the back-half of the roll-cage in Top Fuel Dragsters (although some Funny Car teams adopted this) to prevent any debris from entering the cockpit.
At present, final drive ratios lower than 3.20 (3.2 engine rotations to one rear axle rotation) are prohibited, in an effort to limit top speed potential, thus reducing the perceived level of danger.

References

★ "The Top Fuel V8", Race Engine Technology, #009, p60-69

★ "Running The Army Motor", Race Engine Technology, #008, p18-30

★ "Top Fuel by the Numbers, By John Kiewicz, Motor Trend, February 2005

External links

★ 'Fuel Dragster History from 1950 to 1979. 56,000+ photos'

★ 'Restored Top Fuel Dragsters from the 60s & 70s'

★ NHRA National Hot Rod Association Website

★ WSID Website

★ 'IHRA International Hot Rod Association Website'

★ 'Santa Pod Raceway' - the home of European Drag Racing