• The NHRA has strict guidelines regarding engines for dragsters and other racing vehicles in its jurisdiction.dragster engine image by Robert Young from Fotolia.com
  
  The National Hot Rod Association, or NHRA, is the official governing body of drag racing, with authority reaching more than 200 classes of vehicles in 12 categories. Each category of drag racing has its own requirements regarding the competitors' engines, including allowable engine size, modifications and fuel type.
  
  

Top Fuel Dragsters and Funny Cars

• All top fuel dragsters and funny cars are required to run on a 500-cubic-inch adaptation of Chrysler's Hemi engine, equipped with a supercharger and fuel injection system. This engine employs a multistage, timer-activated clutch instead of a transmission and runs on nitromethane fuel during a race.
  
  

Pro Stock Cars

• The engine in pro stock cars can be no larger than 500 cubic inches, using two carburetors. The fuel utilized is spec gasoline, and more exotic fuels are not allowed.
  
  

Pro Stock Motorcycle

• This category allows a wide variety of engine types, including V-Twin engines like those on Harley-Davidson motorcycles, and inline four-cylinder Kawasaki motorcycles. V-Twin entries are limited to engines no bigger than 160 cubic inches, and four-cylinder entries can't have engines larger than 101 cubic inches. Fuel injection is allowed in both engine types, although the only allowable fuel is spec gasoline.
  
  

Top Alcohol Dragsters and Funny Cars

• Top alcohol dragsters run on methanol instead of nitro or use an injected nitromethane fuel combination. They also rely on a three-speed transmission instead of the multistage clutch system. Top alcohol funny cars are limited to methanol only.
  
  

Comp

• The comp category encompasses 87 different classes of vehicles with a wide variety of engine specifications. Engines in comp range from turbo-charged four- and six-cylinder engines to V-8s and even nitrous-oxide-equipped dragster motors. Engine specs vary from one class to the next.
  
  

Super Stock Cars

• The range of modifications allowed on the engines in super stock cars is extremely wide, with the only regulations being that the car must retain the correct engine block, cylinder heads and carburetor for its make, model and year.
  
  

Stock Cars

• Stock car racing is similar to super stock, only considerably more strict. Alterations are limited to a minimum, especially in the engine. The only modifications allowable for the engine are a basic balancing and rebuild, and a few performance enhancements. Otherwise, the engine must retain its stock cylinder heads, intake manifold and carburetor or fuel injector, which must all be correct to the make, model and year of the vehicle.
  
  

Super Comp

• Super comp cars are primarily dragsters and are given virtually no restriction on engine, chassis or body modifications, provided the vehicle meets NHRA safety standards.
  
  

Super Gas Cars

• Super gas car entries are usually full-bodied cars or street roadsters with no dragsters allowed. Much like super comp racing, there is virtually no restriction on engine specifications provided the vehicle meets all NHRA safety standards. However, super gas cars are prohibited from using any fuel other than gasoline.
  
  

Super Street Cars

• Much like super comp cars, super street cars have almost no restriction on engine specifications provided they meet NHRA safety standards. They must, however, be full-bodied cars.