Understanding Class Racing – Stock Eliminator

Many people attending an NHRA or IHRA event may watch Class racing and wonder what all the letters and classes mean on a car, and how they get there. Well, I’m here to help you.  Class Racing refers to the eliminators of Competition, Stock, and Super Stock.  All three have a multitude of individual sub-classes, classes, and rules.  We’ll start with probably the simplest of the three–NHRA Stock Eliminator.

Click here for the Stock Eliminator class rules on the NHRA website.

Stock is for 1960 and newer factory production automobiles and some sports cars.  In most circumstances, there must have been 500 of that particular model produced, and had been showroom available and in the hands of the general public.  In other words, anyone could go down to their local dealer and order/buy one.  There are some exceptions.  The OEM (original equipment manufacturer) can apply for special production runs of 50 cars to be permitted.  An example would be the 1964 Ford Thunderbolt Fairlanes.

Photos By Bill Truby

Calculating NHRA Spec Weight And Classification

All cars are classified by using the factory shipping weight, divided by either advertised factory horsepower, or NHRA-rated HP.  I will use my car as an example, a 1992 Oldsmobile Toronado Trofeo.  It has a factory shipping weight of 3,444 pounds, and a factory horsepower rating of 170.  3,444/170 = 20.56.  This will classify me into the DF/S (D Front wheel drive/Stock) class.  All cars are classified this way, into one of 51 classes of Stock Eliminator.  Classes run from AA/S and AA/SA (AA/Stock and AA/Stock Automatic) down to W/S and W/SA for rear wheel drive cars and trucks, plus five front wheel drive classes AF/S to EF/S.

AA/Stock would be for the highest factory rated horsepower cars.  Some Mopar Hemis, 440’s and Max Wedges, big block 427 Fords, 427 and 396 Chevrolets, as well as some newer cars – LS-1 Firebirds, supercharged Cobra Jet Mustangs and the new DragPack Hemi Dodge Challengers are in this category.  Cars with a shipping weight/horsepower ratio of 7.50-7.99 pounds will fall into AA/S.  W/S is for four cylinder cars only, with a weight to horsepower ratio of 24 or more.  NHRA publishes their Classification Guide on their website;  you can look up your car to see what class it can fit.  Cars not listed in this Guide are not eligible for Stock Eliminator.

Minimum Weights

Once you find what class your car runs, you can determine the minimum weight for your car.  All cars have a minimum weight they must meet at the scales, with driver.  Cars are permitted to move to the “top” of their class, or move up one class, or move down one class.  Using my car as an example, the weight break for it is 20.56, which puts it into DF/S, designed for cars with a weight/HP ratio between 19.00 and 24.99 pounds.  I can move to the top of the class, which would be 19.00, multiplied by the NHRA rating for the motor, still being at 170.  From there, 170 pounds are added to each car, to arrive at the minimum Class Weight.  So, 19 x 170 + 170 = 3,400 pounds.  If I cross the scales at less than 3,400, the run is disallowed if in qualifying, and I would be disqualified if it occurs during eliminations.

In some cases, NHRA will rate the engine higher or lower than the factory rating, to bring it in line with other cars in it’s class.  As stated above, most classes have many different brands competing in it.  In an attempt to keep the playing field level, NHRA will adjust certain combinations, which can in turn affect the class(es) a car can run.  For example, a 2002 Pontiac Firebird with an LS-1 346 motor started out with a factory rating of 310, and would have fit C/SA.  It now has a rating, by NHRA, of 364, and it now fits A/SA.

Some cars have been de-rated by NHRA, if they are not competive in the class that they would otherwise run.  An example of this is a 1967 Plymouth, with a 440 cid motor and a single four barrel carburetor.  It was factory rated at 375;  NHRA rates it now at 350.  In both cases, you would use the NHRA rating of the motor to determine classification – shipping weight divided by NHRA rating to determine the “natural” class of the car.

My car, being a natural DF/S, can adjust weight to either make the “top” of DF/S, move up to CF/S, or move down to EF/S.  In all cases, it is the “top” weight break of each class, multiplied by NHRA rating and add 170 pounds to determine the minimum weight each car must meet for each class it can run.  Cars also have to pass a fuel check at the scales, to insure racers are not using any illegal additives to their fuel.  Leaded racing fuels are the only ones permitted, and there is an Accepted Fuel list and those are the only fuels legal in NHRA competition.

Qualifying and Racing in Your Class Index

Cars qualify based on how far under their Class Index they can run.  Many years ago, cars ran based off of the National Record for their class.  When participation started dwindling, the Index system was developed.  Originally designed to be an average of all the cars in that class in the country, now almost every car can run quicker than that Class Index, some as much than one-second under or more.  The AA/S Index is the quickest in Stock at 10.60, while  the W/SA Index is 16.65.  The further under that mark you can run in qualifying, the further up the qualifying sheet you will be.  The maximum number of cars that will qualify is 128, with the exception of the U.S. Nationals in Indianapolis, where everyone gets to run.

Once qualifying is complete, the ladder is set, using a standard sportsman ladder where the top half is matched against the bottom half.  In a 128 car field, it would be 1 vs 65, 2 vs 66, 3 vs 37 and so on, down to 64 vs 128.  Once the eliminations start, it is run like a bracket race — with a few exceptions.  Remember the index I told you about?  All cars must dial-in at or quicker than their class index.  Meaning, you better have a certain level of performance in your car.  My car, in DF/S has a Class Index of 15.60.  If the car is hurt and can only run about a 15.80, I still have to dial no slower than the 15.60 Index.  So you don’t want to show up with just a street car with some gears and slicks.

If, in the first round I am matched against a AA/S with my car, and I dial-in at 15.00 and the AA/S dials a 9.75, I get a 5.25 second head start.  Bracket rules, with breakouts and handicaps apply for all runs, unless two cars of the same class run each other.  If two AA/S cars run each other, there is no dial-in, no handicap.  Heads-up, first to the finish line wins (except in redlight situations).  So you want to make sure you have a pretty quick car, for the times you may have a heads-up class run,  but it better be legal.

Tech Inspection, Teardown and Legal Modifications

At some National events, there can be a Tech Inspection teardown.  Cars will be chosen at random (or in the case of a protest) to teardown.  Teardowns vary at times, but usually a head will be pulled, possibly a rod and piston and other items.  Cars must not exceed factory specs.  Camshafts must retain factory lift numbers, though any duration is allowed. Crankshafts can be balanced, but not lightened beyond OEM specs.  Cylinder heads may not be ported, neither can intake manifolds.  Rod and/or piston assembly can not be lighter than factory specs. Valves can not be larger than OEM.  Carburetors and fuel injection throttle bodies can not exceed factory specs either.  Certain aftermarket and replacement parts are allowed, but must meet the weight, volume, and other dimensions of OEM parts.

Wheelbase must meet manufacturers specs, +/- 3/4 of an inch.  Slicks are limited to 9″ wide.  Hood scoops are not permitted, unless that combination (car/motor) came with one.  All this can be checked, and racers found not compliant with the rules will be disqualified from the event, and possibly further action can be taken, depending on the flagrancy of the violation.  In some cases, a multi-month or even full year suspension can be issued; this ensures legality of all cars.

Class Run Offs

At certain designated National events (and all SPORTSnational events), class run offs are held as kind of a race-within-a race, held on Thursday or Friday, before the main Stock Eliminator show.  All cars run against each other, to determine the fastest car.  If there are eighteen B/SA cars there, it will be five rounds of Class Eliminations, to determine who is the baddest of the bad.  At these events, certain class winners, plus a few random cars, are chosen to be torn down.  At Divisional and National Open events, drivers are eligible to set a Class National Record.  Racers must break the record, and run within 1% of it to become the new record holder.  Anyone setting a National Record has to be torn down and pass before receiving credit for the record.

So all in all, Stock Eliminator is a double-edged sword in it’s attraction to racers.  For those who like to run fast and be the top dog, you can set records and go out to win your class.  If you like testing your driving and bracket racing ability against some of the best drivers in the world, you can do that too.  Many of the top bracket racing artists in the country also own and race a Stock Eliminator car and do quite well. Hope this helps you to better understand the Stock Eliminator racing we do.  Future stories, will better explain other issues involving Class Racing.

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