The technology and the attention to detail that goes into building a state-of-the-art Pro Stock engine is virtually unmatched in all of motorsports. It can take hundreds of hours to prepare a single set of cylinder heads or an intake manifold and most successful Pro Stock teams devote the majority of their resources to the area of engine development. Although lightweight engine components and exotic metals are banned, virtually anything else is legal in a Pro Stock engine as long as it maintains its original two-valve per cylinder configuration and does not exceed the 500-cubic inch maximum.
All the power in the world isn't much good if it can't be applied to the race track, which is why a substantial amount of development also goes into building a Pro Stock chassis. Underneath the body, a modern Pro Stock car features a fully-sprung four-link rear suspension, adjustable electronic shock absorbers, and spring-loaded wheelie bars. The roll cage not only protects the driver in the event of an accident, but also serves as an integral part of the chassis.
If has often been said that a Pro Stock car is one of the most difficult cars to drive in all of drag racing. Indeed, Pro Stock drivers stay plenty busy during each six-second run. Beginning with a carefully orchestrated pre-race procedure that includes a tire heating burnout, a Pro Stock driver carefully inches his car to the starting line. Reacting to the first hint of a yellow light from the Christmas tree, the driver quickly releases the clutch pedal and then must make four separate gear shifts. Each shift must be perfectly timed in order for the car to achieve maximum performance. As if staging, leaving the starting line and shifting wasn't enough, a Pro Stock driver must also concentrate on keeping the car as straight as possible during the run before finally deploying the twin parachutes which slow the car from over 200-mph at the end of each quarter-mile run.
ANATOMY OF A PRO STOCK CAR
Rolling ChassisA modern Pro Stock chassis is hand fabricated from rigid 4130-chrome-moly steel tubing for both strength and safety. The wheelbase of a Pro Stock car varies slightly from 105 inches for the Chevy Cobalt and Pontiac Grand Am to 104 inches for the Dodge Stratus. Although a Pro Stock car is much shorter than a 300-inch Top Fuel dragster, the chassis requires more tubing (400 feet) because of the complexity of the roll-cage and suspension design. A basic Pro Stock chassis costs approximately $90,000, which includes front struts and spindles, steering assembly, form-fitting seat, aluminum interior, engine mounting plates, transmission mounts, rear springs, a four-link rear suspension, driveshaft, rear-end housing, and wheelie bars. Other items include front and rear brakes, throttle, brake and clutch pedals, fuel cell, radiator, gauges, tachometer, seat belts, window net, parachute mount, parachute-release lever, wiring, and plumbing. By itself, a chassis weighs approximately 1,000 pounds.
Body
Pro Stock chassis builders utilize either a steel roof and rear quarter panels or a high strength carbon fiber replica. All remaining body components, including the hood, front fenders, splash pans, valance panels, rear deck lid, hood scoop, and doors, are made of fiberglass or other lightweight material. The rear spoiler is manufactured from aluminum.
One area where Pro Stock teams can gain a performance advantage is through improved aerodynamics. However development in that area is limited since all Pro Stock bodies must conform to NHRA body templates that are based on strict specifications supplied by each manufacturer
Engine
The engine choice for most Pro Stock competitors is the GM corporate big-block, though the Chrysler Hemi, and the Ford SVO wedge engine are also common. Engine displacement is restricted to a maximum 500 cubic inches. A Pro Stock engine must also be a 90-degree V-8 design with a single camshaft, and the engine type must be the same corporate make as the body. Engine blocks must be made of steel, although aluminum cylinder heads and intake manifolds are permitted.
Aftermarket engine blocks, such as the GM Merlin, which is designed and cast with OEM approval, are allowed. Pro Stock cylinder heads are some of the most sophisticated components in any form of motorsports. A properly prepared set of cylinder heads may require as many as 300 hours of porting and preparation after extensive research and development. Compression ratios in Pro Stock engine often run as high as 17-1.
Feeding the fuel to the engine is a pair of highly modified four-barrel carburetors and a sheet-metal intake manifold, hand built to conform to the flow requirements of the cylinder-head design. A competitive Pro Stock engine produces upwards of 2.5 horsepower per cubic inch, an amazing figure for their size. A complete Pro Stock engine can cost in excess of $150,000.
Drivetrain
Pro Stock clutches utilize multiple discs and must be serviced after every run to maintain critical tolerances that can mean the difference between a good run or severe tire shake.
Nearly as important as horsepower, proper clutch adjustments are a critical element in producing competitive elapsed times.
Pro Stock drivers use a manual five-speed transmission, and each individual gear shift must be performed by the driver. The clutch pedal is used only for launching the car, not for shifting gears.
Suspension
Pro Stock cars are required to use automotive-type suspension systems. Since the 1970s, front suspensions have utilized McPherson-type struts with hand-fabricated control arms. For rear suspensions, the design of choice is the four-link, evolved from earlier efforts with ladder bars and three-links. The four-link is a nearly infinitely adjustable version of the ladder-bar and allow crew chiefs to compensate slight changes in track conditions. Coil-over shock absorbers is used at both front and rear and can be adjusted to fit the characteristics of each track surface.
Brakes
Four-wheel disc brakes made by aftermarket manufacturers are used in conjunction with dual parachutes to slow Pro Stock car after 200-mph runs. The brakes have single calipers on the front and double calipers on the rear and are usually manufactured from a carbon fiber composite material.
Tires
Pro Stock cars have rear tires almost as big as those on Top Fuel dragsters and Funny Cars; they are 17 inches wide and range from 102 to 104 inches in circumference. Air pressure is as low as 4 1/4 pounds on the rear tires to improve traction and as much as 32 pounds on the front tires to reduce rolling resistance.
Fuel
Pro Stock cars are restricted to racing gasoline (octane rating: 118), which is tested and certified by chemical analysis at NHRA events. The use of fuel additives is prohibited. Pro Stock fuel systems flow the gasoline into the engine at a rate of 7 1/2 gallons per minute.
Driver Safety Equipment
A fire-resistant driving suit, including gloves and shoes, must be worn, as must a certified helmet, and a 360-degree neck collar. Drivers must be secured in the cockpit with a five-point restraint system utilizing belts that are a minimum of three inches wide and a crotch strap. A window net is mandatory. Funny Car-style roll cages have been added to Pro Stock chassis designs to provide further protection.
Additional specifications
A Pro Stock car must weigh a minimum of 2,350 pounds, including driver. The cars must be 2000 model or later two-door coupes or two-door sedans (domestic or foreign). Rear spoilers cannot be longer than 14 inches, 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.
