Sprint (Full Size)
Sprint cars began in the USA in the 1930s and 40s as modified Model T racers and evolved into purpose built cars over the 30 years that followed. Their development paralleled the Midget race car, but Sprints were based on full-size cars. The designs evolved to use V8 engines and eventually wings and roll cages.
Modern amateur cars have advanced in terms of technology, but the racing has the same premise: Drive as quickly around a dirt or paved oval race track. They are characterized by their scratch-built single seat chassis, high power 8 cylinder front-engine, rear-drive layout, encompassing roll cage and big roof-mounted wings to give large amounts of downforce.
Racing is run in the USA, UK, Canada and Australia on local tracks, with the largest racing participation in the USA. In the UK, New Zealand and Australia there are also cars which run on dirt tracks called "Stock Cars" which bear many similarities to Sprint cars, including front engine/rear drive and large roof-mounted wings.
|Power and Weight Stats|
|Horsepower (Typical Range)||600-1050|
|Race Weight (Typical Range)||635-681 kg
Design and Construction
Build Your Own Sprint Race Car
Due to the scratch-built nature of sprint cars, you should be knowledgeable in handling, chassis, suspension, powertrain, aerodynamic and safety design. 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. Much of the design work is iterative, meaning re-designing areas based on new changes to another area. After the iterations are completed, the design will be complete and optimized.
Understanding the handling and suspension of the live axle configuration and the springing/damping aspects are especially helpful in the design and tuning of sprint race cars. Aerodynamics also play a vital role in producing a fast car.
Weight Distribution: Because sprint cars run on oval tracks as opposed to road courses, they are generally configured to optimize counter-clockwise or left turns. Therefore weight distribution must be optimized to obtain as much traction force from all four tires as possible while making left turns.
Suspension: Maximizing the compliance with the track is of key importance. Axle, 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.
The cars use stagger (larger outside tire) and offset (right side tire farther from the chassis than left side) to manage weight transfer, as well as ride height and springs/shocks. Adjustability in these areas must be designed into the car or tuning options will be very limited. At any given track, at any given race, the surface conditions might dictate tuning of these suspension components to provide more/less "bite" and tightening or loosening the rear of the car (understeer or oversteer).
The suspension link locations impact the chassis design.
Chassis: Providing openings to make internal components accessible for maintenance is also important.
Aerodynamic: Sprint cars usually restrict the dimensions and camber of their wings, as well as end plates and gurney flaps (wickerbill). There may be opportunities to maximize downforce and minimize drag through simulations of various wing shapes and attack angles. Depending on the length of the track, changes to wing shape and angle of attack may have a pronounced effect on downforce/drag. Downforce generated by the front and rear wings will affect front and rear grip levels, and will be impacted by the wake of the cars in front. Designing a large range of adjustability into the wing angle of attack will provide maximum flexibility to tune at the track.
Safety: Modern sprint cars require a full roll structure integral to the chassis, with a racing seat/harness. A fuel safety cell, fire wall, and front/side/rear bumper bars for impacts are also mandatory.
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.
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Ensuring the chassis is dimensionally accurate and straight is key. The use of a solid, flat and level build space is important. Jigs are often used in this case to ensure that structural tubing stays in alignment during welding/brazing.
The builder should have solid joining and metal working knowledge and skills when fabricating the chassis/rollcage/suspension. While mild steel (1018/1020) is very forgiving, some metals are best welded using a specific method (mig/tig) and some require heat treatments before and following welding to restore their toughness and strength.
Many components for an amateur-built sprint car can be sourced from sprint parts manufacturers. In some cases, where permitted by regulations, parts can be sourced from production cars. This will lower the overall cost. Components that are specific to racing are also generally what cause the build costs to rise, but many components must be of a racing design, such as a fuel safety cell and therefore care must be taken not to "Go cheap" in the wrong places. If there is no discernible advantage to the construction/materials/weight of a racing part versus an OEM part, then the OEM part may be the way to go.
Because the car is scratch-built, there will be significant effort in design and construction. There is however, an equally great satisfaction and sense of accomplishment at being one of the few people in the world who have built their own race car from the ground up! Many race car manufacturers also started this way, with the development of their own chassis leading them to build cars for others.
Tires and fuel probably form the largest consumable expenses. Powertrain rebuilds and potentially crash repairs will be periodic expenses. Depending on the level of horsepower, rebuilds may be frequent. However, if you are able to perform the labour yourself, the cost will be considerably lower.
Transportation and Support Equipment