The SGS guys all put the limit of HP of the 4.6 just over 500 rwhp. I know a guy that SGS has tuned up to 530 on the stock block and his car is still fine. I know its close. I am ready to buy a shortblock should it happen.The 06 has even more and they are basically the same internals so chances are his will go before mine and maybe I'll get a little advance notice. Man does it feel strong though !!