[griston64]

What psi are you running ?

The problem isn't exactly the excess boost itself, but the heat and detonation caused by the boost. When you shove more air into the cylinder, you have to shove enough fuel in there to keep the proper fuel mixture. If you have more fuel than air, they mixture leans out and burns super hot. The heat can cause hot spots which lead to detonation and pre-ignition. The heat and shock forces from the detonation eat away at the head gasket causing the leak.