C Sports Racer (CSR) now known as Prototype 1 (P1) is a class in the Sports Car Club of America.
it consists of open top prototype style cars.
The maximum displacement is 1615cc, in a 2 valve crossflow engine, with a minimum weight of 1300lbs w/driver.
Supercharging and turbocharging are permitted within limits, and with a maximum displacement of 765cc.
Some CSRs are Formula Atlantic or Formula SCCA cars converted by adding bodywork to the chassis.