It gets very involved in the " letter " classes. Stock and Superstock cars run on a class index. NHRA publishes a number that is derived from the horsepower that engine is factored at ( by NHRA ) That is your class index and you cannot run under it in competition.......unless you are facing a car in the same class.
Stock allows for limited enhancement of parts. Heads cannot be ported and stock or accepted stock replacement parts for the rotating assembly.
Cams must run the same lift for a given engine , but duration and overlap are subject to what the engine builder thinks will work the best.
Superstock is far more exotic in terms of what is allowable..... extreme porting , as long as the port meets a published volume when done. considerable latitude in intake manifolds , valve lobe relocation , cam shafts themselves. Again accepted pistons ,and rods must weight a certain amount depending on the engine.
Same deal with class index.
Competition Eliminator is one of my personal favorites......essentially pounds per cubic inch , though they have rules regarding allowable carburetors. But they are the pinnacle of performance ( not longevity ) because they use vast amounts of unobtanium and every trick in and out of the book to make more power.
They have class indexes too and if a driver runs too quick too often , they entire class has the index reset , so there is a good bit of gamesmanship in the class. But here is where you can see a roadster lined up against a door car or dragster. There are classes within competition eliminator for the widest variety of cars and some of the sickest engine combinations in drag racing.
Super street , super gas and super comp all run on a class index that changes with altitude and atmosphere. based on 10.90 for S/ST , 9.90 for S/G and 8.90 for S/C. Run what you brung , but run the number. These guys have e.t. and reaction time packages that literally cannot be duplicated without electronics like throttle stops , delay boxes , trans brakes etc. Wide mix of car styles , but possibly the least exciting to watch unless you really pay attention to the class. Lots of nuance in a good run and frequently jockeying at the stripe where the margins of victory are perhaps the thinnest in drag racing.
Top Dragster and Top Sportsman is a very expensive form of bracket racing .....that is an over simplification. But they haul the mail on a dial in , or e.t. selected by the driver or crew. Weight breaks depending on which form of propulsion is used i.e. N/A small block 1900 lbs , Nitrous small block 2000 lbs. N/A big block 2350 lbs. etc.
But these cars are fast and expensive.
