Get some APR, you can torque them tighter and not have to worry about the head lifting at high RPMs since there a stronger grade. That's most likely the problem. Use the torque spec they give you. I believe for my car it was around 60ft lbs on stock studs and with ARP I could go up to 80 - 85lbs.

Also you should re-torque the studs after a couple of heat cycles.