Here's some info (long read) on Top Fuel. I didn't know that all the engines were Hemi based!
Facts about Top FuelBefore their run, they do a burnout. This is done for three reasons (water is applied to initially break traction, allowing the tires to spin up). First, it heats the tires up, creating a sticky superficial layer of rubber on the tires. 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 lbf (53 kN) when the car reaches a speed of about 325 mph (523 km/h).
Top Fuel dragsters are notorious for the deafening amount of noise their engines create at full throttle. They generate 120 dB of noise,[1] 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.
[edit] The fuel
NHRA regulations limit the composition of the fuel to a maximum of 90% nitromethane (as of 2008); 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 (but not in the world) to break 300 mph (480 km/h) in the 1/4 mile in March, 1992. Bernstein took his dragster over 300 mph (480 km/h) using a mixture of 90-to-100% nitromethane at the time. Despite nitromethane having a much 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. The laminar flame speed and combustion temperature are higher than gasoline 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 pre-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" cam lift. 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 (8194 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 has been tried but its use is limited due to cost. Valve sizes are around 2.45" (62.2 mm) for the inta ke 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 studs.
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 a luminum 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.
