Don Yenko, who had been racing Corvettes, could not compete successfully against the Carroll Shelby Mustangs after they arrived on the scene; he therefore decided to race modified Corvairs, beginning with the 1966 model. As the stock Corvair did not fit into any of the SCCA categories, Yenko had to modify four-carburetor Corsas into "sports cars" by removing the back seat; in the process he would introduce various performance improvements.