Jon.
I don't think I would recommend your method to anyone. Heating water in a confined space is very similar to throwing aerosol cans in the campfire. You may get away with it, but is it worth the risk?
As for the numbers you are throwing around here. you may want to look up the melting point of aluminum before trying to raise the water to 2500f.
I suspect that the water in your cylinder never reached a very high temperature. As soon as the head gasket began to leak, most of the energy would be used in converting the water to steam.
Anyway, I applaud your ingenuity and I'm amazed that you did not do yourself some severe injury.
Ron