Like their winged counterparts, USAC 410ci sprint cars are open-wheel, open-cockpit machines powered by a naturally aspirated, methanol-injected overhead-valve American V8 engine displacing 410 cubic inches (6.7 liters). The cars weigh approximately 1,400 pounds including the driver and produce over 900 horsepower, yielding a power-to-weight ratio that exceeds contemporary Formula 1 cars. Top speeds can exceed 160 miles per hour depending on track and gearing.
The defining characteristic of the USAC class is the absence of wings. Where winged sprint cars rely on aerodynamic downforce from top and front wings to generate traction, USAC cars run without this aerodynamic aid. The result is different handling characteristics: the relative lack of mechanical and aerodynamic grip makes the cars more difficult to control through corners and creates a distinct driving style that many observers regard as the traditional form of sprint car racing, dating to the class's origins in the 1930s and 1940s.
Sprint cars of both types lack conventional transmissions. They use only an in-or-out gearbox and a quick-change rear differential for gear-ratio adjustment. There is no electric starter; cars are push-started and carry no electrical system beyond the ignition magneto.
USAC, founded in 1956, took over sanctioning of major American open-wheel racing from the American Automobile Association (AAA) and has governed the 410ci National Sprint Car Championship throughout its history. The series races on both paved and dirt ovals, reflecting the historical roots of sprint car competition across surface types. USAC also sanctions smaller regional wingless series: the USAC East Coast Sprint Cars, USAC Southwest Sprint Cars, and USAC West Coast Sprint Cars, which absorbed the Sprint Car Racing Association (SCRA) to form the USAC/California Racing Association (USAC/CRA).
The wingless sprint car is considered the traditional form of the discipline. Many local tracks that run non-wing programs impose rules mandating steel engine blocks and limiting displacement to 305 cubic inches in order to contain costs, but the USAC National championship runs the full 410ci formula.
Because USAC 410ci cars generate no aerodynamic downforce, their mechanical setups differ substantially from winged sprint cars running the same engine displacement. Gear ratios are tuned for lower RPM ranges, and shock, spring, and chassis setups are calibrated for different traction levels. Tire compounds are also different. The driving technique demands earlier rotation and a greater reliance on throttle modulation than winged cars, which can use the wing's downforce to carry speed through corners.
The USAC sprint car program has long served as a proving ground for drivers moving toward the top levels of American motorsport. Indianapolis 500 winners including A.J. Foyt, Mario Andretti, Johnny Rutherford, Parnelli Jones, Johnnie Parsons, Al Unser Sr., and Al Unser Jr. all competed in sprint car racing, as did NASCAR Cup Series champions Jeff Gordon, Tony Stewart, and Kyle Larson. USAC's multi-division structure, which also includes the Silver Crown and Midget championships, allows drivers to build experience across a range of open-wheel formats on the path to higher-profile competition.
The USAC 410ci Sprint Car Championship preserves the wingless sprint car tradition at the national level at a time when the winged World of Outlaws format has become the dominant strand of the sport commercially. For many participants and fans, the wingless car represents an authentic connection to sprint car racing's historical roots, demanding car control and racecraft that the additional downforce of a winged car partially supplants.