In order to determine in which class a certain vehicle should compete and how adjustments in horsepower ratings affect that same program, the NHRA Tech department has developed a step-by-step program in helping to define the proper classifications for both Super Stock and Stock.

1. Find the car in the classification sheets. These can be found here; if further assistance is needed, contact the NHRA Technical department.

2. Find the body style that will be utilized. After the correct body style has been determined, follow over to the engine package being used. After you find get the correct body and engine, you will find the class weight break

3. Look in the NHRA Rulebook for the class weight breaks. This will correspond with a certain class-letter designation. This will be the vehicle's base (or home) class. NHRA allows a vehicle to run in its base class or drop down one letter class. This means if the base class is C, the car can run C or D. If a competitor chooses to run in the lower class, his/her weight will have to be changed to fit into that class.

4. NHRA allows a competitor to run at the minimum in the class. To find minimum weights for the classes, take the factored horsepower and multiply it by the minimum weight break in that class. The factor number is located at the bottom of the NHRA Stock Car Classification Guide. The proper class weight will then be determined by dividing this figure by the horsepower or performance rating of the engine used. Class is determined without driver weight. Once classification is calculated, 170 pounds will be added for driver weight to arrive at the minimum weight.

An examples of these steps using Stock eliminator:

Step 1: 1976 Buick Regal
Step 2: Body style - 2-door coupe
Engine - (factory) 350cid with 155hp
NHRA factor - 235 horsepower
Step 3: Class weight break of 16.43.
Referencing this in the Rulebook, the car would fall into the "P" range of 16.00 to 16.99.
Step 4: Class "P" minimum weight = 235 (NHRA factored horsepower) x 16.00 (class minimum weight) + 170 (set driver weight)

To run in class "P," the car's minimum weight is 3,930 pounds.

To determine minimum weight by moving down a class:
Class "Q" minimum weight = 235 (NHRA factored horsepower) x 17.00 (class minimum weight) + 170 (set driver weight)
To run in class "Q," the car's minimum weight is 4,165 pounds.

During the season, some horsepower factors are adjusted by either adding or subtracting from the respective engine packages. This is done in an effort to keep the vehicles and classes on a level playing field. When this is done, the factor found in the NHRA Stock Classification Guide will change, therefore possibly putting the car into a different base class.

For example, using the same vehicle as before, with an additional 10 horsepower and a reduction of 10 horsepower from the factored power you can refigure the class and minimum weight:

Additional horsepower example:
The 245 horsepower has a class weight break of 15.76
Referencing this in the Rulebook, the car would fall into the "O" range of 15.00 to 15.99.
Factor: Class "O" minimum weight = 245 (NHRA factored horsepower) x 15.00 (class minimum weight) + 170 (set driver weight)
To run in class "O" the car's minimum weight is 3,845 pounds.

Reduction horsepower example:
The 225 horsepower has a class weight break of 17.16
Referencing this in the Rulebook, the car would fall into the "Q" range of 17.00 to 17.99.
Factor: Class "Q" minimum weight = 225 (NHRA factored horsepower) x 17.00 (class minimum weight) + 170 (set driver weight)
To run in class "O," the car's minimum weight is 3,995 pounds.