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Dragracing – lining up next to the other guy and seeing who’s got the beststuff – remains an incredibly popular sport, for both spectators andparticipants. Although multi-lap circle track and road racingcompetition may have received the lion’s share of media attention overthe past several years, mashing the throttle and driving to the finishline is good business.

According to some recent (admittedlyunscientific) polls on our website, our readers are excitedabout the upcoming drag racing season. When asked “Which racing seriesare you most looking forward to in 2011?” nearly half of therespondents said NHRA racing, more than twice the next highest number.

Accordingto some recent information from various motorsports industry groups,there are well over 150,000 active drag racers in the United States.And from the response the Engine Builder staff saw at the recentInternational Motorsports Industry Show in Indianapolis, IN, andPerformance Racing Industry Trade Show in Orlando, FL, they have alldecided “economy-shmonomy” – it’s time to go racing again.

Dragracing engines run the gamut from 5-hp junior dragsters to nearly10,000-hp nitro burning Top Fuel cars. In between, there are hundredsof engine combinations that find their way under a hood, onto thestreet or strip – often starting in your shop first.

Sportsmanand bracket racing offer a great deal of potential to engine builders,say industry experts. Sportsman racers are slugging it out at littlestrips on Saturday nights, getting ready for their real jobs during theweek then doing it all again next week, so they depend on YOURexpertise to maximize their investment. A durable, consistent enginewill go a lot further than one that makes a lot of power but can’tstand up to repeat runs.

Racing Classes
“There are manyorganizations that sanction drag racing in the United States, but thetwo main organizations are the National Hot Rod Association (NHRA) andthe International Hot Rod Association (IHRA),” says Engine Buildercontributor Jim Walbolt. “While other groups may have their owncompetition rules, nearly all abide by either NHRA’s or IHRA’s safetyrules.”

There are more than 200 classes of vehicles featured in NHRAcompetition (IHRA has similar categories). Those classes are groupedinto 12 categories, or eliminators, each strictly governed by NHRA rulemakers. Class eligibility is based on various requirements andspecifications, including type of vehicle, engine size, vehicle weight,allowable modifications and aerodynamics.

We’ll leave the Proclasses out of this discussion (but we won’t abandon it entirely – wehope to feature Pro engine builders in print and online in 2011) and give a brief explanation of some ofthe Sportsman classes and some further explanation of someengine-specific rules.

Competition Eliminator
Comp, whichboasts nearly 100 classes, showcases a variety of gas-burningdragsters, altereds, street roadsters, coupes, sedans, and truckspowered by engines ranging from turbocharged inline four cylinders tohigh winding small block Chevy V8s to 700-cid gas carbureted gasburning “mountain motors.” Some are supercharged, others turbocharged,but most are carbureted. A handicap starting system equalizescompetition.

Super Stock

Super Stock features an array ofstock-appearing foreign and domestic factory automobiles and sportscars with limited modifications. More than 80 classes of cars andtrucks, from late-model sedans and passenger vehicles to vintage musclecars from the 1960s and 1970s, are showcased. A handicap startingsystem equalizes competition, and breakout rules apply.

Stock Eliminator
Stockencompasses a variety of foreign and domestic production vehicles.Everything from late-model passenger cars and trucks to the popularvehicles of the 1960s and 1970s can participate in any one of Stock’s100 classes. Few modifications or alterations are allowed. As in SuperStock, a handicap starting system is used, and breakout rules areenforced.

Super Comp
Super Comp features one class ofvehicle and is the quickest of the three Super classes. Made up mostlyof gas-burning dragsters, though full-bodied production vehicles androadsters are eligible, Super Comp features heads-up competition on an8.90-second index. Engine modification is virtually unlimited.

Super Gas
Super Gas features mostly full-bodied production vehicles with fullfenders, hoods, grills, tops, windshields, and functional doors.Left-hand-steering street roadsters are allowed, but dragsters are not.The class is governed by the same rules as Super Comp; only the indexis different. A heads-up start is used, but racers may not run quickerthan the 9.90-second index.

Super Street
Super Street, designed as an entry-level category. It is reserved forfull-bodied production vehicles, including sports cars, vans, andtrucks with full fenders, hoods, grills, tops, windshields, andfunctional doors. Racers compete on a 10.90-second index.

Here are some specific rules from NHRA as they relate to the Stock and Super Stock classes:

Stock Cylinder Heads
Must be correct casting number for year and horsepower claimed, perNHRA Technical Bulletins or NHRA accepted. Porting, polishing, welding,epoxying and acid-porting prohibited. Combustion-chamber modificationsprohibited. Cylinder heads are additionally restricted in that theymust retain original-size valves at original angles +/- 1 degree andmust be able to hold original cylinder-head volume per NHRASpecifications.

Runner volumes may not exceed the current SuperStock cylinder-head volumes as listed on Regardless ofthe poured volume measurement, any modifications to intake or exhaustrunners prohibited. Any evidence of modifications from the originalcastings will be grounds for disqualifications as determined by NHRA inNHRA’s sole and absolute discretion.

Any aftermarket steel valve permitted, must retain stock headand stem diameters. Only engines OEM-equipped with sodium-filled valvesmay use sodium-filled replacement valves. Titanium is prohibited.Hardened keepers are permitted. Lash caps are prohibited.Valve-diameter tolerance: +.005? or -.015? from NHRA Specs.

The following are prohibited: spark-plug adapters; cylinder-headstuds; any grinding in ports or combustion chambers; removal of anyflashings; sandblasting or any other modification to cylinder heads;any film coating of intake and exhaust runners; any film coating ofcombustion chamber.

Runners and combustion chamber must retain OEM appearance. Final acceptance is determined by NHRA at their discretion.

Intake side of head may not be cut into any part of the valvecover bolt holes. Heat riser passage may be blocked from intakemanifold side of cylinder head. Blocking passage down in valve pocketprohibited.

The following are permitted: polylocks, jam nuts, screw-inlarger-diameter rocker studs or pinned studs, bronzewall valve guides.Valve spring umbrellas optional. Cylinder head may have all of theseats replaced. Any valve job permitted, O-ringing prohibited. Exhaustplates prohibited.
Must be same year and make as the vehicle, aftermarket NHRA-acceptedcylinder blocks are permitted. Equipment other than originalfactory-installed is prohibited. Any special equipment export kit(superchargers, dealer-installed options, etc.) automaticallydisqualifies the car.

Engine must remain in stock location — height, setback, etc.Cylinder bores must not exceed .075? over stock. Bores are measured atthe top of the cylinder where ring wear is not evident. Crossbreedingparts is prohibited.

Normal balance job (i.e., one piston/rod assembly untouched)permitted. Otherwise lightening of component parts is prohibited. Allcarburetors, manifolds, heads, etc. must be tightened to prevent anyair or fuel leaks. Vacuum lines must be securely connected or blockedoff.

Stroke tolerance is +/- .015?. Stock OEM crankshaft ismandatory. Lightening of the crankshaft other than normal balance jobis prohibited.

Cylinder blocks may be sleeved. Aftermarket SFI Spec 18.1harmonic balancer mandatory in AA/S through G/S and AA/SA through G/SA.

Super Stock Cylinder Heads
Must be correct casting number for year and horsepower claimed, perNHRA Technical Bulletins or NHRA-accepted. Cylinder head casting mustalso be on NHRA runner volume list as published in National Dragsterand on
Porting, polishing, welding, epoxying, and acid-porting is permitted.Grinding and polishing in combustion chamber permitted. Welding and/orapplying epoxy in combustion chamber prohibited. Spark-plug hole mustmaintain the stock location, size, and angle as machined by the OEM;spark-plug adapters prohibited.

Valve-guide centerlines must maintain the stock lateral andfront-to-back location as machined by the OEM. Valves must maintainstock angle; valvestem angle must remain stock, +/- 1 degree. Cylinderhead must be able to hold combustion chamber, intake and exhaust runnervolumes per NHRA Specifications. Any aftermarket steel valve permitted;must maintain stock head and stem size; titanium valves prohibited.(OEM sodium-filled valve may be replaced with titanium, provided weightis equal to or greater than original.) Valve diameter permitted to be+.005? or -.015? from published NHRA Technical Bulletins.

External modifications prohibited. Welding or epoxying permittedon external portion of runners for repair only, maximum 2 runners perhead. Heat riser passages may be blocked off from intake-manifold sideof cylinder head or in exhaust port. The following are permitted:polylocks, jam nuts, screw-in or pinned studs. Any valve job accepted.Exhaust plate permitted between header and cylinder head, maximum 1/2?;may not protrude into exhaust port. Cylinder head may have all seatsreplaced.

Must be same year and make for car used, aftermarket NHRA-acceptedcylinder blocks permitted. Equipment other than originalfactory-installed prohibited. Any special-equipment export kit(superchargers, dealer-installed options, etc.) automaticallydisqualifies car.  

Engine must remain in stock location, cylinder bores must notexceed .075? over stock. Bores are measured at top of cylinder wherering wear is not evident. Crossbreeding parts prohibited. Normalbalance job permitted. Otherwise lightening of component partsprohibited.

Carburetors, manifolds, heads, etc., must be tightened toprevent air or fuel leaks. Vacuum lines must be securely connected orblocked off. Stroke tolerance is +/- .015?. Stock OEM or NHRA acceptedaftermarket crankshaft mandatory.

Aftermarket crank must retainOEM configuration; i.e., billets, knife edging, etc., prohibited.Lightening of crankshaft other than normal balance job prohibited.Cylinder blocks may be sleeved. Aftermarket SFI Spec 18.1 harmonicbalancer mandatory. Timing-belt covers optional.

Walbolt reminds us that if you’re interested in working withsanctioning bodies OTHER than these, you’ll need to be familiar withtheir rules. In some classes, internal engine modifications may beunlimited, while in others those modifications may be strictly limited.

Other racing bodies include the National Mustang RacersAssociation (NMRA), the largest Ford focused drag racing group in theUnited States. It recognizes 14 different classes, and has rulesspecific to each.

The National Muscle Car Association is another drag racingorganization that recognizes 1950 and newer American production carsand trucks. NMCA recognizes multiple classes including the Pro Stockclass.

The NMCA Pro Stock Class is a naturally aspirated class designedfor 1950 and newer American production cars and trucks that areequipped with stock-type chassis and 10.6? wide tires. Pro Stockentries can use small block and big block engines up to and including amaximum of 525 cid (depending on combination). Pro Stock permits avariety of race-proven modifications and performance enhancements onstock bodied, stock appearing vehicles.

Winning in Sportsman drag racing doesn’t always mean coming infirst – consistency and reliability are demanded. Knowing the rules isa plus.”Sportsman

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Doug Kaufman
Doug Kaufman has been with Babcox Media since 1987 serving in a variety of editorial and publishing roles and titles. He is currently publisher of Engine Builder. He also has been editorial liaison between Babcox and the National Association for Stock Car Auto Racing (NASCAR) for the past 12 years. Doug has a Bachelor of Science in Journalism from Bowling Green State University and remains a committed MAC enthusiast.