Sport Racer/Sports Prototype
The Sport Racer (and the leading edge Sports Prototype) is an evolution of the sports cars that were raced after World War II. The designs began to change from that of road-going sports cars to the purpose-built racing machines we see today in endurance racing and the 24 hours of Le Mans.
Modern amateur sport racer cars are characterized by their scratch-built single or double seat chassis, mid-engine rear-drive layout and full-covering aerodynamic bodywork. Many sport racers use wings and underbody venturi tunnels to provide downforce that enables much higher cornering speeds
Amateur racing classes for sport racers generally focus on designs which use a spaceframe chassis, 4 to 6 cylinder car or motorcycle engine, and fiberglass bodywork. The chassis is relatively easy to construct and repair and the engine is reasonably low cost to maintain.
Racing is generally on road course circuits and is therefore most popular in parts of Europe and the Americas where road course circuits are found.
Sport Racer/Sports Prototype Contents
|Power and Weight Stats|
|Horsepower (Typical Range)||150-225|
|Race Weight (Typical Range)||612-681 kg
Design and Construction
Race Car Models of This Type
Examples of sport racers include SCCA P1/P2 (C Sport/D Sport/SR1/SR2) , 750 Racers,
Build Your Own Sport Racer/Sports Prototype
Due to the scratch-built nature of sport racers, the designer must 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.
Weight Distribution: Having a good static weight distribution is important. Typically the front will be lighter in front/rear weight distribution. Left/right weight distribution should be as close to 50/50 as possible, as sport racers are used on left/right turning road course circuits.
Suspension: Maximizing the contact patch of the tires with good suspension geometry is of key importance. 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. The suspension pickup point locations impact the chassis design.
Chassis: Maximizing torsional rigidity is important to keep the handling responses consistent. Providing openings to make internal components accessible for maintenance is also important, and quite often at odds with the needs to maximize torsional rigidity. The cockpit opening in a spaceframe often presents the greatest challenge to achieving a high torsional rigidity.
Aerodynamic: Aerodynamics on sport racers is very important. Where engine power is very similar, the slipperier the bodywork and the more efficient the downforce, the better a car will perform. Front downforce is generated through shaping of the nose section to create a high pressure flow above the nose, and a corresponding low pressure flow under the nose section. This can take the form of an integrated wing type structure or an airdam. Central downforce is usually generated via venturi tunnels where allowed. Rear downforce is generated through diffusers and wings, tuned to maximize the benefits of both. Converging the rear bodywork gradually has the advantage of reducing drag where long straights are part of the racing circuit.
The overall balance of the car is affected by the front, underbody and rear aerodynamic performance so the positioning of these aero devices must be considered. Turbulence generated upstream will also have an effect on the performance of aero devices further back on the car. For maximum flexibility, aero devices should have a wide operating range and adjustability if possible.
Minimizing the drag created by the bodywork and wings is important to maximize speed on straights.
Safety: Providing a substantial crash/rollover safety cell for the driver is vital along with a racing seat and multi-point harness. Protection for fuel storage, fire protection, and nose and side crumple zones for impacts.
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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Due to the precision that is associated with the tuning and performance of sport racers, 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 sport racer can be sourced from small production cars (i.e. Mini) instead of being fabricated if doing so is acceptable. 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 high quality, such as a fuel safety cell and therefore care must be taken not to "Go cheap" in the wrong places.
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!
Consumable costs are reasonable in relation to other race car types—Tires probably form the single largest consumable expense. Engine rebuilds and crash repairs may be more significant than other race car types, depending on the engine type and frequency they occur.
Transportation and Support Equipment