Porsche first attempted to compete in the 1980 Indianapolis 500 with an engine initially based on the 935 sports car flat 6 with Interscope Racing as the entrant and Danny Ongais as driver. The engine would be fitted to Interscopes's new Interscope IR01, which featured a tubular rear subframe, as the Porsche motor could not be used as a stressed member as the Cosworth engines were. USAC had more favorable rules for stock-block engines at the Indy 500 than CART allowed at their races. Porsche applied to and received approval from USAC for their engine to be allowed the stock block boost pressure of 55 inches. After setting an unofficial lap record in private testing at the now-defunct Ontario Motor Speedway, a clone of the Indiana track, rumors circulated regarding the performance of the engine and top-level teams pressured officials to alter their initial ruling and now categorize the Porsche a race motor, dropping boost pressure to 48" thus losing its boost and horsepower advantage. Porsche withdrew and Interscope entered a Parnelli VPJ6C-Cosworth DFX at Indianapolis that year. The Indianapolis engine became in the basis of the highly-successful 956/962 motor.