I've got an F1D on my 07 5.3, stock bottom end, running 9lbs at 6000rpm on E85. Made 630 rwhp. Been good for a couple thousand miles now. No reason 550-600 shouldn't be safe. I don't feel like I would push mine much further though due to the stock crank snout.

 

Longblue what is done to the top end of your motor? And whatvfuel system

 

PRC 2.5 243 heads, EPS 218/226 .601 cam, ls7 lifters, comp trunnions.

Fuel is twin 450 Walbros in stock bucket. ID1300 injectors. Holley fuel rails on NNBS intake.

 

LongBlue can you post up a pic of your intake and fuel rail setup

 

Had to make my own hold down brackets for the Holley rails. Each rail is fed individually and exits individually to fpr.