The NHRA has a huge variety of categories and eliminators. Class eligibility is based on requirements that include type of vehicle, engine size, vehicle weight, allowable modifications and aerodynamics.
Top Fuel, Funny Car, Pro Stock, Top Alcohol Dragster, Top Alcohol Funny Car, Super Comp, Super Gas, Super Street and Pro Mod feature a single class of vehicle in heads-up competition. Comp, Super Stock, and Stock are made up of a variety of classes equalized by a handicap starting system. Top Dragster and Top Sportsman feature a single class of vehicle in bracket-style competition.
Top Fuel Dragsters are the quickest accelerating race cars in the world. The fastest competitors reach speeds of 335 miles per hour in only 3.64 seconds. Because of the high speeds, this class exclusively races only a 1,000 foot distance, and not the traditional ¼ mile.
These 10,000 hp. machines are powered by supercharged and fuel-injected 500-cubic-inch adaptations of the Hemi engine. Top Fuel dragsters can burn up to 15 gallons of fuel in a single run (since 2015, NHRA regulations limit the composition to a maximum of 90% nitromethane; the remainder is largely methanol). Constructed of chromoly steel tubing and carbon-fiber composite, Top Fuel cars are 25 feet long and weigh 2,330 pounds in race-ready trim.
At maximum throttle and RPM, the exhaust gases escaping from a dragster's open headers produce about 900-1,100 pounds-force of down force. The massive airfoil over and behind the rear wheels produces much more, peaking at around 12,000 pounds-force when the car reaches a speed of about 330 mph. The engine generates around 150 dB of sound at full throttle, enough to cause physical pain or even permanent hearing damage.
The massive rear "wrinklewall" slicks are constructed in such a way as to allow the sidewall to be twisted by the torque applied at launch, softening the initial start and thus reducing the chances of breaking traction.
After each run, a Top Fuel engine must be completely torn down and rebuilt in only 75 minutes. This is because a Top Fuel engine starts tearing itself apart as soon as the driver releases the clutch.
Similar to their Top Fuel counterparts but with a shorter wheelbase Funny Cars are characterized by having tilt-up fiberglass or carbon fiber automotive bodies over a custom-fabricated chassis, giving them an appearance vaguely approximating manufacturers' showroom models. The engines can only be V8s displacing no more than 500 cubic inches. The fuel mixture is usually 85–90% nitromethane and 10–15% methanol.
Funny Cars are almost as fast as Top Fuel Dragsters and can run in the 3.8-second range with speeds in excess of 330 mph. They are powered by the same supercharged and fuel-injected 500-inch engines as Top Fuel dragsters. Like Top Fuel Dragsters, the engine must be rebuilt after each run.
Top Alcohol Dragster
The Top Alcohol Dragster class was devised in the 1970s as a replacement for the Top Gas class, which was similar but burned gasoline. Initially, alcohol dragsters competed against Funny Cars in a category known as Pro Comp.
Top Alcohol Dragsters can be powered by a supercharged methanol-burning engine or an injected nitromethane combination. The injected nitro cars do not use a transmission, and the supercharged cars have three forward speeds. Weights vary according to combination but are generally between 1,975 and 2,125 pounds. Performances can be in the 5.1 sec. range at more than 285 mph.
Top Alcohol Funny Car
Top Alcohol Funny Cars look similar to Fuel Funny Cars, with about half the power of a Top Fuel car. They are restricted to the use of methanol fuel and have a three-speed transmission. Top Alcohol Funny Cars feature basically the same chromoly steel chassis as the nitro cars and are fitted with the same carbon-fiber replica bodies. Top Alcohol Funny Cars are capable of performances in the 5.3 sec. range at more than 270 mph.
The Pro Mod Drag Racing Series features an eclectic mix of vehicles that range from ’41 Willys coupes to ’63 Corvettes to late-model Ford Mustangs and Dodge Vipers, and few classes offer as much diversity and excitement. The engine choices are equally as diverse; competitors can use superchargers, turbochargers, or nitrous-oxide injection and can run into the high-five-second zone at speeds of more than 250 mph.
Pro Stock cars are some of the most technologically advanced machines in drag racing. The class, that emerged from Super Stock in 1970, is often described as "all motor." Built around a carbon fiber body, Pro Stock cars must conform to precise measurements and weigh no less than 2,350 pounds. Pro Stock engines use electronic fuel injection and 118 octane gasoline and are restricted to a maximum of 500 cubic inches. They can make in excess of 1,300 horsepower. A competitive Pro Stock car can run in the 6.5 sec. range at more than 210 mph.
No category in NHRA competition features more variety than Comp. Dragsters, altered, street roadsters, coupes, sedans, front-engine nostalgia dragsters, sport compact cars, and trucks race in 75 classes. The engine combinations are just as diverse as the vehicles, from turbocharged four- and six-cylinder engines to Pro Stock-style V-8s and nitrous-oxide-equipped mountain motors. Most cars are classified using a formula that divides total car weight by cubic inches. Each class is assigned an index based on what a well-built car should run, and races are handicapped according to those indexes.
Top Dragster, Top Sportsman
Essentially a pair of categories for fast E.T. racers, Top Dragster presented by Racing RVs (open-wheel entries) and Top Sportsman presented by Racing RVs (full-bodied cars) feature a qualified field of 32, 48, or 64 entries. Competitors may choose their own dial for eliminations provided it is not slower than 7.99 seconds (8.19 in Divisions 6 and 7). Eliminations in both classes are run using a traditional bracket racing format with a full three-amber Christmas Tree start, and the breakout rule is enforced. It is not uncommon for entries to run in the sixes at more than 200 mph.
The quickest of the heads-up Super classes (8.90 index), Super Comp is composed primarily of dragsters. Engine, chassis, and body modifications are virtually unlimited. Four- and six-cylinder-powered entries may have a minimum weight of 1,000 pounds; all others cannot weigh less than 1,350 pounds. Most Super Comp cars are capable of running well under the 8.90 index but use a number of electronic aids, including a timer and adjustable throttle, to run close to the index without running quicker than it, or breaking out.
Super Gas entries, which run on a 9.90 index, are primarily full-bodied cars and street roadsters. No dragsters or altered are permitted. Rules regarding engine and chassis modifications are extremely liberal, though the use of exotic fuels is prohibited. The minimum weight is 2,100 pounds except for four-cylinder-powered cars, which may have a minimum weight of 1,200 pounds. As in Super Comp, competitors use electronic timers and throttle stops to run as close to the class standard without going under. Also as in Super Comp, races are staged using a four-tenths Pro start.
At NHRA Lucas Oil Drag Racing Series races and select NHRA Mello Yello Drag Racing Series events, Super Street racers compete on a fixed 10.90-second index. All vehicles must be full-bodied cars and weigh no less than 2,800 pounds except for six-cylinder cars, which may have a minimum weight of 2,000 pounds, and four-cylinder- and rotary-powered cars (1,200 pounds). Engine and chassis modifications are virtually unlimited. Racers compete on a five-tenths Pro Tree.
Super Stock vehicles may look like ordinary passenger vehicles, but they are highly modified race cars. The category features primarily late-model sedans and vintage muscle cars, and entries are classified using a system that divides factory shipping weight by NHRA-factored horsepower. Significant engine modifications are permitted, but the vehicle must retain the correct engine block, cylinder heads, and carburetor. Cars are handicapped using an index system, and the breakout rule is enforced.
Stock cars are similar to Super Stockers, but the rules regarding everything from engine modifications to body alterations are much stricter. Virtually any car is eligible to compete, and entries are classified using a system that divides factory shipping weight by NHRA-factored horsepower. Bodies must be unaltered and retain a full factory interior. Tires are limited to a maximum 9-inch-wide rear slick. Engines must be correct for the make and model vehicle and must retain stock cylinder heads, intake manifold, and carburetor. Modifications are limited to a basic balancing and rebuild with only a few performance enhancements.