Have done some modification's to my 2001 500EFI'S. Would like to know how much fuel pressue the stock injector's can handle. Also is there any advantage to increasing the stock fuel pressue on stock injector's?

I have the stock injectors out of 502 Mags and have had the fuel pressure as high as 65 psi under full boost. No problems after 40 plus hours. They make over 750 hp and 850 ft lbs.

The only reason to increase fuel pressure is to compensate for lean running conditions. To measure exact air/fuel ratio's you need to have oxygen sensors installed and monitor them as you are running/tuning.