[Barnsnake]

If the water cannot circulate within the engine when the thermostat is closed it will heat up unevenly. It is likely the water in the heads will be boiling before the water contacting the thermostat is anywhere near the temperature required for it to open.

Removing or drilling large holes in the thermostat will resolve the uneven heating issue, but it will cripple the thermostats ability to accurately control the engine temperature. The engine will be slow to warm up or may never reach proper operating temperature. If all you do is race on hot afternoons, that's fine, but every other engine should have a functional thermostat and a circulation bypass.