[Tcoat]

Originally Posted by Capt Spaulding

This strikes me as a band-aid, rather than a solution. Something changed that led to the behavior OP is experiencing. My reading of the OP's posts suggests everything was working fine for a period of time and then, suddenly, it wasn't. I don't think the spring in the radiator cap weakened enough to lead to this. A higher pressure cap may raise the threshold of coolant ejection, but I don't think it will solve his problem.

I still have a nagging voice that whispers "head gasket." The HC test should have ruled that out, but... It may be getting close to time to bring Full Blown in on this.

@OP: Have you talked to FBM yet?

I still see nothing that shows head gasket. The car is modded beyond the ability of the stock components. They need to be upgraded to deal with the mods.