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Based on the gains we saw through the simple changes that were made on Jay’s ’13 Pony, optimism about reaching or going beyond the 700 rear-wheel-horsepower mark was high when Jay installed the tiny 69mm pulley. As expected, the small wheel works like gangbusters. However, despite removing a 90mm idler pulley and installing a 100mm pulley to hopefully maintain belt traction, belt slip—and its resultant boost loss—came on when engine speed went above 7,000 rpm and we found the ‘Stang’s stock fuel pump was at its limit. After several pulls in which the engine pulled really hard before falling off, we decided to revert back to the 72mm idler pulley.