NHRA Classes Overview
Top Fuel, Funny Car, and Pro Stock are just three of the more than 200 classes of vehicles featured in NHRA competition. Those classes are grouped into 12 categories, or eliminators, each strictly governed by NHRA rule makers. Class eligibility is based on various requirements and specifications, including type of vehicle, engine size, vehicle weight, allowable modifications, and aerodynamics.
The four Professional categories are Top Fuel, Funny Car, Pro Stock, and Pro Stock Motorcycle. They, along with Top Alcohol Dragster and Top Alcohol Funny Car and the three "Super" classes – Super Comp, Super Gas, and Super Street – feature a single class of vehicle in heads-up competition. The remaining categories – Comp, Super Stock, and Stock – are made up of a variety of classes and use a handicap starting system to equalize competition.
Among the fastest-accelerating machines in the world, 7,000-horsepower Top Fuel dragsters are often referred to as the "kings of the sport," and with good reason. They are capable of covering a quarter-mile in 4.4 seconds at more than 330 mph. Powered by a supercharged and fuel-injected 500-cubic-inch adaptation of the famed Chrysler Hemi engine, Top Fuel dragsters can burn up to 15 gallons of nitromethane fuel during a single quarter-mile run. Constructed of chromoly steel tubing and carbon-fiber composite, Top Fuel cars are 25 feet long and weigh 2,250 pounds in race-ready trim.
Similar to their Top Fuel counterparts but with a shorter wheelbase and a carbon-fiber body that loosely resembles a production-based automobile, Funny Cars routinely run in the 4.7-second range and are capable of speeds in excess of 330 mph. Funny Cars are powered by the same supercharged and fuel-injected 500-inch engines as Top Fuel dragsters. Funny Cars are also similar to Top Fuel dragsters in that they do not use a transmission but rather transmit power to the huge Goodyear rear slicks through a multistage clutch assembly that is activated by timers.
Often called "factory hot rods" because of their resemblance to production-based automobiles, Pro Stock cars are some of the most technologically advanced machines in drag racing. Built around a sophisticated tube chassis and four-link rear suspension, Pro Stock cars must conform to precise measurements and weigh no less than 2,350 pounds. Pro Stock engines use two carburetors and spec gasoline and are restricted to a maximum of 500 cubic inches. They can rev to more than 10,500 rpm and make in excess of 1,300 horsepower. A competitive Pro Stock car can run in the 6.6s at more than 208 mph.
Pro Stock Motorcycle
These highly modified vehicles, which can run under seven seconds at more than 195 mph, feature a purpose-built tube chassis and a lightweight, aerodynamically enhanced replica of original bodywork. The class features a wide variety of makes, models, and engines, including V-Twin entries from Harley-Davidson and Buell and inline four-cylinder-equipped Suzuki and Kawasaki models. To ensure a level playing field, pushrod-equipped V-Twin engines are limited to 160 cubic inches, and the high-winding four-cylinder engines cannot be larger than 101 cubic inches. Fuel injection is permitted, and spec gasoline is the only fuel allowed.
Top Alcohol Dragster
Top Alcohol Dragsters may look like Top Fuelers, but they have significant differences. Whereas Top Fuelers use supercharged, nitro-burning engines, Top Alcohol Dragsters may use 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 2,050 pounds. Like Top Fuelers, Top Alcohol Dragsters are restricted to a maximum wheelbase of 300 inches. A typical run is in the 5.2s at more than 270 mph.
Top Alcohol Funny Car
Similar in physical appearance to their nitro-burning Funny Car counterparts, Top Alcohol Funny Cars 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, though the Top Alcohol Funny Car bodies do not need as much downforce and use a much smaller rear spoiler. Top Alcohol Funny Cars are capable of performances in the 5.5s at more than 260 mph.
No category in NHRA competition features more variety than Comp. Dragsters, altereds, street roadsters, coupes, sedans, front-engine nostalgia dragsters, sport compact cars, and trucks race in 87 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.
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. The top class is SS/AH, which is exclusively for '68 Dodge Dart and Plymouth Barracuda factory race cars. Cars are handicapped using an index system, and the breakout rule is enforced.
Stock cars are similar to their big brothers in Super Stock, 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 nine-inch-wide rear slick. Engines must be correct for the make and model vehicle and must retain stock cylinder heads, intake manifold, and carburetor or fuel injector. Modifications are limited to a basic balancing and rebuild with only a few performance enhancements.
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, though all entries must adhere to NHRA safety standards. 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 altereds 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 POWERade 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.