I make 510/381 on my ef4 @ 33 psi. It's all about not being an idiot with big stock block power. That means regularly maintain the motor, don't load up the motor in fifth gear, don't be at 33 psi 24/7 and your motor will stay happy for years.

 

I made 585awhp @ 32psi on a ported BB-BBK-C Turbo on e85 with zero issues. I beat the **** out of my car and it always ran like a rapped ape.

 

Nice thread found out some important tips on running stock block with upgraded turbo