Production Stock Car (Showroom)

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Stock Car (Production-Based)

The production-based stock car (Sometimes referred to as a "Showroom Stock", "Street Stock", "Super Stock" or just "Stock Car") is a race car built on a production chassis from a car manufacturer. These cars are the original "Stock Car", and got their start in the hands of moonshiners in the USA who were attempting to outrun the authorities with their illegal liquor. They took production cars (including police cars), increased the power and lightened the chassis to provide the speed edge required over the police.

The same cars were raced at first informally and eventually in small organized races. Following American prohibition, the racing continued and until the 1970s stock car racing was built around modified production cars.

The production-based stock car is characterized by a production chassis with an engine mounted at the front which drives the two rear wheels and incorporating a roll-cage structure to protect the driver.

Depending on the class, the vehicle may be close to stock or modified heavily.

Variations of the stock car concept are used on dirt and paved ovals as well as paved road courses. Racing events have are held on circuits worldwide.

Power and Weight Stats
Horsepower (Typical Range) 100-500
Race Weight (Typical Range) 1225-1589 kg
2700-3500 lb

Design and Construction

Race Car Models of This Type

Traditionally production cars built using a front engine-rear drive layout

Build Your Own Production-Based Stock Car

Knowledge Level

When modifying a production-based car to perform in oval or road course racing, you should have at a minimum working knowledgeable in handling, chassis, suspension, powertrain, aerodynamics and safety. These six major areas of the car design work as an integrated unit and the designer must have an understanding of how changes to one area affect the others.

Depending on the class you wish to participate in, the regulations will limit the modifications you can make. However, having a sound working knowledge that enables you to modify the car in the best possible way is important. One vital area will be the roll structure, which if not available off-the-shelf will require you or a speed shop to fabricate.

To get the most from your car, you should have advanced knowledge in the areas of handling, suspension and powertrain, which represent the key areas to extracting the maximum performance on either dirt or pavement. If aerodynamic changes are permitted, this may also become an important area of study.

Design Challenges

Weight Distribution: Typically the front will be heavier in front/rear weight distribution due to the front-engine configuration. Weight distribution that is almost balanced Front/Rear is desirable, so positioning components rearward to counter engine weight will help achieve this. Static left/right weight distribution may be adjusted depending on the type of circuit (Oval versus road course) via positioning of internal components such as the battery, oil tank, oil cooler and fuel cell.

Suspension: Stock suspensions may have limitations on adjustability, but higher classes allow more extensive changes to, or replacement of the stock suspension. Choosing a donor car with good suspension adjustability may save a lot of work later, but even with limited adjustability there is still the opportunity to learn and adjust before spending more money to upgrade a car.

Maximizing the contact patch of the tires with good suspension geometry is of key importance especially on high grip surfaces like pavement. Having a range of adjustability for caster, camber and toe are useful in tuning the steering and tracking characteristics. On oval dirt tracks these settings can be tuned to provide better turn-in.

If you are modifying suspension components, ensure play (unwanted movement) is removed by the new components.

Suspension, wheel and tire weights (Unsprung weight) affect the compliance of the suspension, which in turn affects handling, so keeping all these components as light as possible is an advantage. Springs and dampers (shock absorber) must be matched to the suspension geometry and calculated weight transfer forces to provide useful, tunable performance.

Chassis: Adding a roll cage to the chassis may add additional torsional rigidity to the chassis. The additional rigidity will give predictable handling as the chassis will not twist unduly affecting the suspension performance.

Powertrain: Depending on the class, powertrain modifications can include extensive changes to the engine components and driveline components. The goals of changes to the powertrain should be to increase horsepower and engine efficiency. This can be accomplished through replacing stock components for increased internal flow (Intake/exhaust), improved combustion, reducing friction and removing/replacing power robbing accessories. In terms of final drive, any modifications that increase power delivery (ie. Limited slip differentials) to the road should be considered.

Aerodynamic: Front air dams and rear spoilers may be used in some higher classes and are used to generate downforce. On entry-level classes, aero is not going to be as important as driving skill or car setup, which is where the focus of a builder should be initially.

Safety: The production chassis should incorporate a substantial crash/rollover safety cell with racing seat and racing harness and padding around the driver as needed. Depending on the class level, fuel safety is provided via a fuel safety cell while fire protection is provided with an integrated chassis firewall. Front/side/rear impact protection is usually provided by multi-tube structures bolted or welded to the chassis. The glass windows in the cars should be removed as they are of no value in racing. Although production car windows are laminated for safety, their presence can be a potential hindrance to egress for the driver and a hazard if they become dirty or cracked and block the driver's sight.

If you intend to race under a sanctioning body, always read and understand the regulations of your chosen racing class before designing or building any race vehicle.

Design Resources

Learn the basics about race cars and race car design from our free online knowledge series

Download our free race car design aids to assist you designing your race vehicle.

In-depth books and learning resources we recommend for scratch-built stock car design.

Join our forum to ask and find answers to your scratch-built stock car design/construction questions.

Construction Challenges

Most components permitted for entry-level production stock cars are bolt-on type components and therefore are within the mechanical skills of most people. Challenges include the number of components which are changeable, and the difficulty in changing them (i.e. Things like engine removal), which may require specialized workshop tools.

For roll cages that must be custom fabricated, there is the additional requirement of fitting it into a production vehicle and of locating mounting points that do not compromise the uni-body chassis.

Build Costs

The entry-level classes should be economical, with the focus on driving and setup. Improving the cars performance will be limited by regulations, so work within the regs. As you progress into higher classes, with many parts replaceable and new parts permitted, it is quite easy to spend a significant sum of money "hopping up" your race car. However, with adequate knowledge, it is possible to select areas of modification that provide maximum value and still keep costs to a minimum.

Build Effort

Build effort depends on the number of areas that are modified. If your modifications are performed a little at a time, the effort will also be manageable.

Racing Cost

Consumable costs are low, with the highest expense likely coming from the purchase of racing tires and fuel. Body damage repairs may also factor.

Transportation and Support Equipment

The vehicle will need to be trailered to the track.

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