Here's one for you

[das]

when I rev up my engine the cap blows off the coolant overflow what do you think bad head?

 

[SoHK_alumni]

I'd first guess a blown head gasket but a cracked head is certainly a possibility as well.

 

[MtrJunkie]

Head or head gasket, the gasket being my first guess. Do you have any oil in the coolant or does it smell like gas? You're putting a ton of stress on the cooling system, so I wouldn't run it anymore like that. I'd do a compression and leak down test on it to find the problem.