I have trick flows and never drill any of mine. I run at 180-200 all day long.

 

I think it's more of a precautionary thing than anything else. Aluminum heads on a cast iron block are more prone to warping if you overheat, and potential steam pockets at the top of the block won't help the issue. But then, if your cooling system is adequate, I don't suppose it'll make much difference. I imagine plenty of Trans Am motors were flogged without these holes drilled, and I bet they worked just fine.

 

Gotcha, that makes sense. I guess I'm lucky that I have a good cooling system because I didn't know they needed to be drilled.