Inside the NHRA: Automatic Horsepower Factoring System (AHFS) explained

The AHFS is used to review and evaluate runs in Stock and Super Stock for possible horsepower adjustments. The review is conducted twice per racing season. The two reviews are compiled individually so the data is not cumulative. Runs included in the AHFS database are limited to final qualifying runs (Q data) and final elimination runs (E data) at NHRA national events only. (At events where class eliminations are run, all runs are included in the AHFS database. Only the first round of class is part of qualifying and therefore is part of the "Q" database.) The "Q" data and "E" data files are the official data gathered by the NHRA timing system and processed through the NHRA Information Technology department. NHRA "Q" data and "E" data are the only data files used for the AHFS.

The first review period includes data from national events 1 through 12 and the second period includes runs from events 13 through 23. The following procedure is used in reviewing run data:

Final qualifying, class eliminations, and elimination runs of 1.15 seconds or more, under the index, at NHRA national events will trigger an automatic review. (The combination must make at least two runs of 1.15 or quicker before a review is triggered to prevent a "one time fast run" from triggering the system.) In reviewing runs of 1.15 or more under the index, the database of runs for the engine combination being reviewed are put through three screenings as listed below. The screenings will look for an overall engine family average or class/engine average faster than 1.00-second under. Runs of .50 and slower are not included in calculating the engine or class/engine averages:

Engine family average: The overall engine average for all cars, regardless of class, running the particular engine combination being reviewed are included in this screening.

Class/engine average where engine is run: The class/engine average of the car running the specific combination in the class that triggered the review is studied.

Body style and transmission type: Also considered in the above two screening processes are body style of the engine combination being reviewed and transmission type. Adjustments are only in effect for the specific car model being evaluated. The body style are generally classified by the OEM auto manufacturers' definition of "platform", i.e., the Camaro and Firebird body are both based on the same platform and therefore considered the same with regard to body-style classification. In some instances, however, more than one body style will trigger a review. With regards to transmission type, if the class average triggers the review, the adjustment would be for classes with the type of transmission triggering the change. However, if an engine family average triggers the review, the adjustment would be for all transmission types.

If either the engine family average or the class/engine average are found to be faster than 1.00-second under, a change will be initiated.

To more clearly illustrate how the AHFS program affects a given combination, the following is a hypothetical evaluation in Stock class for a 305-cubic-inch, 215 factory rated horsepower, fuel-injected Camaro during a review period:

Two K/SA Camaros running this combination ran 1.214- and 1.187- second under the index, triggering a review by the committee. As per the procedure outlined above, the overall engine average is analyzed first. Upon reviewing the engine average made by the 305/215/241 FI combination, 10 runs had been recorded (2 in K/SA and 8 in L/SA) with a total engine average of .945-second under. Because the overall engine average did not hit the required 1.00 under, the combination did not warrant a horsepower adjustment based on overall engine average.

The next step, per the procedure outlined above, is a class/engine review. The class of the car that actually triggered the review was K/SA. The class review revealed that K/SA had a class/engine average for the combination in question of 1.201-second under, therefore surpassing the 1.00-second-under requirement and signaling a horsepower adjustment for all 305/215/241 FI Camaros.

An important element to note and one most often misunderstood by racers is that although a K/SA Camaro affected the change, the L/SA 305/215/241 FI Camaros that run this combination also received a horsepower adjustment. The reason is that a specific combination can run in more than one class based on NHRA rules; therefore, all cars with the specific engine combination, transmission and body style will be affected.

Once the need for an adjustment is determined, the following sliding-scale formula, based on a percentage of horsepower, is used to calculate the horsepower increase:

Under Index Horsepower Increase Index Change

1.150-1.299 1.25% -.05

1.300-1.399 2.25% -.10

1.400-or greater 3.25% -.15
(immediate change)

Adjustments are rounded up to the nearest full horsepower even if the fraction is below 0.5 horsepower. As an example, 2.15 horsepower is rounded to 3 horsepower. The quickest run, by the combination being reviewed, is used to determine the adjustment percentage.

Runs of 1.40 or more under the index will be reviewed and adjusted as soon as such runs were made. Runs at divisional events and National Opens are included in the 1.40-second-or-more-under analysis. This is done to better react to any out-of-line indexes or under-horsepowered combinations. Therefore, at all such events, a 3.25 percent horsepower adjustment or index reduction will be initiated immediately. The decision to adjust horsepower or to reduce the index will be at the discretion of the NHRA Tech Department.

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