The AHFS Explained In Detail

[Jim Wahl]

Probably the most controversial subject we deal with in our form of racing. This is very well explained and every racer should read it and even have their own copy as reference. This is directly from the NHRA and is the official explanation.


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 for factor INCREASES is conducted twice per racing season. The two reviews are conducted individually. Data in the 1st review segment is not used for reviews in the 2nd segment and visa-versa. The review for factor DECREASES is conducted once per racing season. The data used during the review for possible reductions in hp is cumulative from the 1st National event through the final National event of the calendar year. Runs included in the AHFS database are limited to final qualifying runs (Q data) and all elimination runs (E data) at all NHRA National, Sports National and LODRS events. (At events where class eliminations are run, all class elimination 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. No runs made during exempt events, National Opens, test and tune, time trials, 1/8th mile events or races within a race (i.e. Jegs Allstar eliminations, Stock / Super Stock Combos or other races that are not part of a season long points championship) are included in any review.

The first review period includes data from National and LODRS events 1 through 12. The second period includes runs from events 13 through 24. The following procedure is used in reviewing run data:

Final qualifying, class eliminations, and elimination runs of 1.00 seconds or more, under the index, at NHRA National, Sports Nationals, and LODRS events will trigger a review. By definition, a trigger run is a run 1.00 second and quicker under the index. The engine family combination must make at least two trigger runs of 1.00 or quicker before a review is conducted to prevent a "one time fast run" from triggering a review. Trigger runs are not required to be in the same class. Multiple trigger runs can be made by the same car at the same event. The engine family combination being reviewed is put through two screenings as listed below. The screenings will look for an average of 0.850 and faster. Runs of .350 and slower are not included in the screening.



1st screening: The average for all vehicles running the particular engine family combination being reviewed is included in this screening. The review process will average runs in ALL classes TOGETHER with the same transmission type & the same body platform.
2nd screening: The average for all vehicles running the particular engine family combination being reviewed is included in this screening. The review process will average runs in ANY specific class SEPARATELY where there are ANY trigger runs.
Parameters used for reviews:

Transmission type: Reviews made with manual transmission combination will be reviewed separately from auto transmission combinations & visa-versa in Stock Eliminator. Reviews made with manual transmission combination will be reviewed separately from auto transmission combinations & visa-versa in Super Stock Eliminator for those cars competing in section 12A (with the exception of SS/AH), 12B,& 12C. All other cars competing in sections 12D – 12G are averaged together with manual & auto transmissions.
Body platform: Both screening reviews are only in effect for the specific car model being evaluated. The body style is 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 platform classification.
GT & base SS classes: GT classes will be separate from base SS combinations & visa-versa.
GT/FWD & GT/RWD: FWD bodies will be separate from RWD bodies & visa-versa.

If the average in EITHER the 1st or 2nd screening is found to be 0.850 or faster, a change will be initiated.



If the average in BOTH the 1st and 2nd screening is found to be 0.849 or slower, NO change will be initiated.


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 engine family being reviewed, is used to determine the adjustment percentage.
Once the need for an adjustment is determined, the sliding-scale formula, based on a percentage of horsepower, is used to calculate the horsepower increase:



To decrease the potential for horsepower/index adjustments when favorable atmospheric (i.e. “mineshaft”) and/or track conditions may have contributed to extraordinary performance the NHRA has developed a system to protect the racers’ horsepower/indexes. If at the conclusion of qualifying the first competitor in the bottom half of the field is -.850 seconds or faster under the class index, the Q and E Data will not be used for the mid-year and year-end reviews. This will only apply to qualified fields of 32 or more cars. Automatic changes due to runs of -1.20 or more under the respective index will still count at these events.


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

1.000-1.099


1.25%


-.05

1.100-1.199


2.25%


-.10

1.200-1.249


3.25%


-.15
(immediate change)

1.250-1.299


4.25%


-.20 (immediate change)

1.300-1.349


5.25%


-.25 (immediate change)

1.350-1.399


6.25%


-.30 (immediate change)

1.400-1.449


7.25%


-.35 (immediate change)

1.450- 1.499


8.25%


-.40 (immediate change)

1.500- 1.549


9.25%


-.45 (immediate change)

1.550- 1.599


10.25%


-.50 (immediate change)

1.600- 1.649


11.25%


-.55 (immediate change)

1.650- 1.699


12.25%


-.60 (immediate change)

1.700- 1.749


13.25%


-.65 (immediate change)

1.750- 1.799


14.25%


-.70 (immediate change)

1.800- 1.849


15.25%


-.75 (immediate change)

1.850- 1.899


16.25%


-.80 (immediate change)

1.900- 1.949


17.25%


-.85 (immediate change)

1.950- 1.999


18.25%


-.90 (immediate change)




Runs of 1.200 or more under the index will be reviewed and adjusted following the event.

This is done to better react to any out-of-line indexes or under-horse-powered combinations. Runs at all NHRA National, Sports National, and LODRS events, including those at altitude-factored racetracks, are included in the 1.200-second-or-more-under analysis. No runs made during exempt events, National Opens, test and tune, time trials, 1/8th mile events or races within a race (i.e. Jegs Allstar eliminations, Stock / Super Stock Combos or other races that are not part of a season long points championship) are included in any review. 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.



Parameters used for reviews of 1.2xx runs are the same as stated above.

The decision to adjust horsepower or to reduce the index will be at the discretion of the NHRA Tech Department.

In addition to reviews resulting in a horsepower increase, a competitor may request (only one request per competitor, per review period.) a review for the purpose of a decrease in horsepower factor or index adjustment. The request must include eliminator, year, model, engine size, advertised horsepower, factored horsepower, and class; to be eligible. (NHRA AHFS Horsepower Request Form).

The screenings will look for an overall engine family average, or class/engine average less than 0.549-seconds under. If both averages are found to be slower than 0.549-second under, a change will be initiated. Runs of 0.100-second under and slower are not included in calculating the engine average:

In addition, the engine family must NOT make two runs of 0.650 or quicker or any run 0.850 or quicker during the past two (2) review periods, for the review to continue. Once an engine family receives a horsepower increase it is not eligible for a decrease.

Parameters used for competitors request for reduction are the same as stated above.

If the average is found to be 0.549 or less, a change will be initiated.
If the average is found to be 0.550 or faster, NO change will be initiated.
The review process will average runs in ALL classes TOGETHER with the same transmission type & the same body platform. The review process will also separate cars by GT & base SS classes, & FWD and RWD combinations.



No runs made during exempt events, National Opens, test and tune, time trials, 1/8th mile events or races within a race (i.e. Jegs Allstar eliminations, Stock / Super Stock Combos or other races that are not part of a season long points championship) are included in any review.



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 decrease:





Under Index


Horsepower Decrease


Index Change

0.166-quicker


1.25%


+.05

0.101-0.165


2.25%


+.10



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. The decision to adjust horsepower or to increase the index will be at the discretion of the AHFS Committee.

[Randall Klein]

Len Imbrogno’s “simple AHFS program” (his words), still explained years later, harmful to spectators, SEMA, vendors and some racers

Take data from eighth mile or quit dicking around

Build it race it or stay home

[James Perrone]

Why the 1/8 mile. ? We all run 1/4 mile.

[Larry Hill]

Most people run hard to the 1/8 and adjust before or after 1000'. Albert Lee beat me in Indy class one year with his Firebird and ran more 1/8 mph than 1/4 mph. However NHRA try's to do it racers will adjust.