Pro Stock Drag Racing is a class of drag racing featuring 'Factory Hot-Rods'. The class can be known as all motor, as there are very strict rules governing the modifications allowed to the engines, and the types of bodies used.

History

The National Hot Rod Association Pro Stock class emerged from the production-based Super Stock class in 1970 with a more liberal set of rules and an absence of handicaps. Rules initially favoured big-block V8s but by 1972 had changed to favour small-blocks to reflect contemporary trends in the American auto industry. However, by the early 1980s the big-blocks returned due to the popularity of faster 'outlaw' Pro Stocks who continued to use that engine combination throughout the 1970s.

Pro Stock today

Engine

• The engine must be manufactured by the same company as the car body. Though no engine currently being raced in Pro Stock is used on any manufacturer's assembly line, all of the raw components are available to anyone. Engine blocks and cylinder heads are often provided in a "raw" condition with only approximate dimensions and rough machining. Each team will continue to machine and modify the part to their own standards.
• If the car is Chevy, the block must be from any General Motors division: for example, if a team wanted to use a Northstar block from Cadillac, they could do so.
• Engine capacity is restricted to a maximum 500 in³ (approx 8.2 L) single-camshaft, 90-degree V-8 However, the IHRA Pro Stocks use 800+ in³ mountain motors.
• Pro stocks are limited to carburetor (naturally aspirated) intake systems, however the intake manifold and heads are open to modification. The most effective intake manifold configuration has continued to be the "tunnel ram" for nearly 40 years. The carburetors are raised above the engine; the length and configuration of the intake passages ("runners") is critical to horsepower output. The tall intake manifolds predicate the large hood scoop that is a signature of the Pro Stock class.

This has resulted in Pro Stock heads being the most sophisticated in any drag racing category.

Pro Stock engines generally produce around 2.5 hp/in³ (114 kW/L). A complete Pro Stock engine normally costs more than $80,000.

Drivetrain

• Pro Stock clutches utilize multiple discs. These must be serviced after every run to maintain critical tolerances that can mean the difference between a good run or severe tire shake.
• Since 1973, the most popular transmission was the Lenco planetary design, first used as a four-speed and now as a five-speed. Although still used in IHRA Pro Stock and in Air-Shifted three-speed units in IHRA Pro Modified, NHRA Pro Stocks utilize a Liberty or G-Force five-speed clutchless manual transmission.

Suspension

• Pro Stock cars are required to use automotive-type suspension systems.
• Since the 1970s, front suspensions have utilized MacPherson struts with control arms; for rear suspensions, the design of choice is the four-link.
• Coil- over shock absorbers are used at both front and rear.

Brakes

• Four-wheel disc brakes made by aftermarket manufacturers are used in conjunction with dual parachutes to slow Pro Stockers after near 200 mph (320 km/h) runs.
• The brakes have single calipers on the front and double calipers on the rear.

Fuel

• The factory hot rods may use only racing gasoline (octane rating: 118), which is tested and certified by chemical analysis at NHRA ([1] www.nhra.com) events.
• Pro Stock fuel systems flow the gasoline at 7.5 US gallons per minute (0.5 L/s).

On top of all of these specifications, each car must:

• Weigh a minimum of 2,350 pounds (1066 kg), including driver.
• The cars must be 1991 model or later two-door coupes or two-door sedans.
• Rear spoilers cannot be longer than 13 inches (330 mm), measured from the body-line-to-spoiler transition point to the tip.
• Complete stock headlights, parking lights, and taillights must be retained in original factory location.

This makes for some incredibly tight racing; the front runners in the class can reach speeds over 200 mph (320 km/h) in 6.7 seconds (approx). The qualifications rounds are only separated by less than a tenth of a second across all competitors. In a particularly tight qualifying roster, the difference from #1 to the final #16 qualifier may be only .05 seconds.