A drag race is an acceleration contest, on a track or drag strip, that begins from a standing start between two vehicles over a measured distance. A drag racing event is a series of such two-vehicle, tournament-style eliminations. The losing racer in each contest is eliminated and the winning racers progress until only one remains.
These contests are started by means of an electronic device commonly called a Christmas Tree because of its multicolored starting lights. On each side of the Tree are seven lights: two small amber lights at the top of the fixture, followed in descending order by three larger LED lights, a green bulb, and a red bulb.
Two light beams cross the starting-line area and connect to trackside photocells, which are wired to the Christmas Tree and electronic timers in the control tower. When the front tires of a vehicle break the first light beam, called the pre-stage beam, the pre-stage light on the Christmas Tree indicates that the racer is approximately seven inches from the starting line.
When the racer rolls forward into the stage beam, the front tires are positioned exactly on the starting line and the stage bulb is lit on the Tree, which indicates that the vehicle is ready to race. When both vehicles are fully staged, the starter will activate the Tree, and each racer will focus on the three large amber lights on his or her side of the Tree.
Depending on the type of racing, all three large amber lights will flash simultaneously, followed four-tenths of a second later by the green light (called a Pro Tree), or the three bulbs will flash consecutively five-tenths of a second apart, followed five-tenths later by the green light (called a Sportsman, or full, Tree).
Two separate performances are monitored for each run: elapsed time and speed. Upon leaving the staging beams, each vehicle activates an elapsed-time clock, which is stopped when that vehicle reaches the finish line. The start-to-finish clocking is the vehicle's elapsed time (e.t.), which serves to measure performance. Speed is measured in a 66-foot "speed trap" that ends at the finish line. Each lane is timed independently.
The first vehicle across the finish line wins, unless, in applicable categories, it runs quicker than its dial-in or index. A racer also may be disqualified for leaving the starting line too soon, leaving the lane boundary (either by crossing the centerline, touching the guard wall or guardrail, or striking a track fixture such as the photocells), failing to stage, or failing a post-run inspection (in NHRA class racing, vehicles usually are weighed and their fuel checked after each run, and a complete engine teardown is done after an event victory).
Air box: Used primarily on Pro Stock Motorcycles, it settles "negative air" around carburetors the way a hood scoop does on a car.
Air foil: The same as a wing – a stabilizer, generally used to create downforce, which increases stability and tire-to-track adherence at high speeds.
Bang the blower: An explosion inside the supercharger caused by a flame from the combustion process accidentally re-entering the supercharger, where fuel and air are present. Generally caused by a stuck or broken intake valve that normally would be closed during the combustion sequence.
Breakout: Used only in handicap racing, "breakout" refers to a contestant running quicker than he or she "dialed" his or her vehicle (predicted how quick it would run). Unless the opponent commits a more serious foul (e.g., red-lights, crosses the centerline, or fails a post-race inspection), the driver who breaks out loses. If both drivers break out, the one who runs closest to his or her dial is the winner.
Burned piston: When a cylinder runs lean (too much air in the air-to-fuel mixture) and excessive heat burns or melts the piston.
Burnout: Spinning the rear tires in water to heat and clean them prior to a run for better traction. A burnout precedes every run.
Christmas Tree: Also called the Tree, it is the noticeable electronic starting device between the lanes on the starting line. It displays a calibrated-light countdown for each driver.
Clutch Can: The bell-shaped housing, or bell housing, used to encase the clutch and flywheel.
Clutch Lockup: The progression of clutch-disc engagement controlled by an air-timer management system.
Deep stage: To roll a few inches farther into the beams after staging. This causes the pre-stage lights to go out. In that position, a driver is closer to the finish line but dangerously close to a foul start.
Dial under: When drivers in Super Stock and Stock (handicap categories) select an elapsed time quicker than the national index. Drivers select a dial-under, or e.t., that they think their cars will run based on previous performance. The breakout rule is in effect.
Diaper: An absorbent blanket made from ballistic material, often Kevlar, that surrounds the oil pan to contain oil and parts in case of an engine explosion; required for Top Fuel, Funny Car, Top Alcohol Dragster, and Top Alcohol Funny Car.
Dropped cylinder: When a cylinder runs too rich (too much fuel in the air/fuel mixture) and prevents the spark plug(s) from firing.
Elapsed time: The time it takes a vehicle to travel from the starting line to the finish line. Also called e.t.
Eliminations: After qualifying, vehicles race two at a time, resulting in one winner from each pair. Winners continue in tournament-style competition until one remains.
Foul start: Indicated by a red light on the Christmas Tree when a car has left the starting line before the green light, or starting signal.
Full Tree: Used in Competition, Super Stock, and Stock, for which a handicap starting system is used to equalize competition. The three amber bulbs on the Christmas Tree flash consecutively five-tenths of a second apart, followed five-tenths later by the green starting light. A perfect reaction time on a full Tree is .500.
Header(s): A fine-tuned exhaust system that routes exhaust from the engine; replaces conventional exhaust manifolds.
Hemi: A Hemi engine has a hemispherical shaped cylinder-head combustion chamber, like a ball cut in half.
Holeshot: When a driver reacts quicker to the Christmas Tree to win a race against an opponent with a quicker e.t.
Hydraulic: When a cylinder fills with too much fuel, thus prohibiting compression by the cylinder and causing a mechanical malfunction, usually an explosive one.
Index: The expected performance for vehicles in a class as assigned by NHRA. It allows various classes of cars in the same category to race together competitively.
Interval timers: Part of a secondary timing system that records elapsed times, primarily for the racers' benefit, at 60, 330, 660, and 1,000 feet.
Methanol: Pure methyl alcohol produced by synthesis; used in Top Alcohol Dragsters and Top Alcohol Funny Cars.
Nitromethane: Produced specifically as a fuel for drag racing, it is the result of a chemical reaction between nitric acid and propane.
Pre-stage: To position the front wheels about seven inches behind the starting line so the small yellow lights atop that driver's side of the Christmas Tree are glowing. The next step is to stage and be ready to race.
Pro Tree: Used in Top Fuel, Funny Car, Pro Stock, Pro Stock Motorcycle, Top Alcohol Dragster, Top Alcohol Funny Car, Super Comp, Super Gas, and Super Street, which feature heads-up competition. All three large amber lights on the Christmas Tree flash simultaneously, followed four-tenths of a second later by the green starting light.
Reaction time: The time it takes a driver to react to the green starting light on the Christmas Tree, measured in thousandths of a second. The reaction-time counter begins when the last amber light flashes on the Tree and stops when the vehicle clears the stage beam.
Sixty-foot time: The time it takes a vehicle to cover the first 60 feet of the racetrack. It is the most accurate measure of the launch from the starting line and in most cases determines how quick the rest of the run will be.
Slider clutch: A multi-disc clutch designed to slip until a predetermined rpm is reached; decreases shock load to the drive wheels.
Speed trap: The final 66 feet to the finish line where speed is recorded.
Stage: To position the front wheels right on the starting line so the small yellow lights below the pre-stage lights are glowing. Once both drivers are staged, the calibrated countdown (see Christmas Tree) may begin.
Supercharger: A crank-driven air/fuel-mixture compressor, also called a blower. It increases atmospheric pressure in the engine to produce more horsepower.
Turbocharger: An exhaust-driven intake air compressor (see supercharger).
Wedge: An engine with a combustion chamber resembling a wedge in shape.
Weight transfer: Critical to traction. Vehicles are set up to provide a desired weight transfer to the rear wheels. Upon acceleration, the front wheels lift and the weight shifts to the rear wheels, which makes them less likely to spin.
Wheelie bar(s): Used to prevent excessive front-wheel lift.