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CATEGORIES (articles) > American Motorsport > Motorsport Events For Petrolheads > Top Fuel Drag Racing

Top Fuel Drag Racing

Clocked Speed = 314 mph (506 km/h), Kwinana Race Track, W.A., 2005

Top-Fuel Racing refers to a class of drag racing in which the cars are run on 85% nitromethane and about 15% methanol (90% nitromethane, 10% methanol under FIA) also known as racing alcohol, instead of gasoline. The nitromethane used to power the engines of top fuel dragsters costs about US$30 per U.S. gallon (US$8/L). Top Fuel dragsters use between 10 and 12 U.S. gallons (38 to 45 L) of fuel for a complete pass, including the burnout, backup to the starting line, and quarter-mile run. The engine generates about 3.4 times as much power as a similar displacement engine running gasoline.

Top fuel dragster time (4.567 sec at 321 mph or 516 km/h)

These cars compete in a 1/4 mile (0.4 km) race and complete it in less than 4.5 seconds at upwards of 330 mph (530 km/h). Top Fuel dragsters are not the fastest linear accelerating vehicles in the world, as evidenced in the following link: 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, and almost 11 times quicker than it takes a production Porsche 911 Turbo to reach the same speed. They can exceed 280 mph (450 km/h) in just 660 feet (0.2 km).

Facts about Top Fuel

Before their run, they do a burn-out. It is done for two reasons. First, after applying some water, it heats the tires up, and secondly, it removes foreign debris from the tires. A top fueler's burnout alone can travel halfway down the track.

At top engine speed, the exhaust gases escaping from the open headers produce about 800 pounds-force (3.6 kilonewtons) of downforce (although much more downforce is produced by the massive foil sitting over the rear wheels). 12,000 pounds ofDownforce generated by the rear wing at 325 mph.

The noise produced by one of these machines can cause deafness in extreme cases.

The Fuel

The fuel is limited to 85% nitromethane (CH3NO2), the rest is essentially methanol. Nitromethane has a stoichiometric air fuel ratio of about 1.7:1 and its energy content is about 11.2 MJ/kg. This suggest a very high specific energy at stoichiometric, about 6.6 compared to about 2.9 for gasoline. It has a high heat of vaporisation, 0.56 MJ/kg, and together with the high fuel flow this provides excellent cooling. Compared to gasoline the laminar flame speed and combustion temperature is higher at 0.5 m/s and 2400°C. Nitromethane can also be used as a mono fuel with a partial burn. This means that 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 nitromethane is used as a SI engine fuel. Rich mixtures make the fuel very difficult to ignite, how rich mixtures that can be used is actually limited by the ignition system. Rich mixtures also increase combustion duration and the exhaust will contain hydrogen (H2) that will ignite because of the high temperature when it comes into contact with oxygen at the end of the exhaust pipes. Nitromethane is also pressure sensitive; meaning that you will get more power with increased engine load. The engine will consume 22.75 gallons of fuel during warmup, burnout, staging, and the quarter-mile run.

Top fuel engines

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 is made out of bespoke parts it retains the basic configuration with two valves per cylinder activated by pushrods from a central placed camshaft. The engine has hemispherical combustion chambers, a 90 degree V angle; 4.8" bore pitch and a 5.4" camshaft height.

The regulations limits the displacement to 500 cubic inch (8193.5 cc), given the 4.8" bore pitch this makes it possible to fit a 4.19" bore. 500 cubic inch and a 4.19" bore hence results in a 4.5" stroke. Larger bores have been tried, but have shown to weaken the block. Compression ratio is about 6.5:1.

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. Like the original Hemi the block has a long skirt, there are five main bearing caps which are fastened with aerospace steel studs; main studs and side bolts. There are three approved suppliers of these blocks the teams can choose between.

The cylinder heads are CNC machined from aluminium billets. In the heads the two valves per cylinder are placed. 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" for the intake and 1.925" 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. Like the mains aerospace steels bolts are used to secure it to the block.

The camshaft is billet steel, made from 8620 carbon steel or similar. It runs in five oil pressure lubricated bearings shell and is driven by gears in the front of the engine. Mechanical roller lifters, steel push rods and steel rockers are used to actuate the cams. 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 is running on a steel roller bearing and the steel rocker arms run on a titanium shaft which runs in 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. These springs doesn't use any interference, it's not required or possible with titanium. Valve retainers are also made of titanium, so is 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.

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. This ring provide 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 ring doesn't seal then. The third ring is an oil scraper ring whose function is helped by the second ring.The con rods are of forged aluminium and do provide some damping. 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, but up to 5.0 bar is possible. The manifold is fitted with a 200 lb 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

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 spill 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 92 gallons/minute at 8000 rpm and 500 PSI fuel pressure. In general 10 injectors are placed 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 engage engine speed drop, and to compensate the air/fuel mixture is enriched. As engine speed then climb the mixture is made leaner.

The air/fuel mixture is ignited by two 14 mm spark plugs per cylinder. These plugs are fired by two 44-amp magnetos driven from the camshaft. Normal ignition timing is 58-65 degrees BTDC. 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, 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. Exhaust temperature is about 260 °C at idle and 980 °C by the end of a run.

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.


Power output of these engines is around 8000 hp. This is calculated from performance as these engines aren't tested on a dynamometer. This would suggest a torque of 3760-4980 lb-ft and also a brake mean effective pressure of 80-100 bar.

Engine weight

  • Block with liners 85 kg
  • Heads 18 kg each
  • Crankshaft 37 kg
  • Complete engine 225 kg.

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 and 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.

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CATEGORIES (articles) > American Motorsport > Motorsport Events For Petrolheads > Top Fuel Drag Racing

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