A friend was having problems cooling a 700hp (555 cubic inch) motor in his street driven Nova. He spoke with the owner of
Waterless Coolant | car radiator coolant|radiator coolant flush who was more passionate about his product than you could imagine.
Outlaying a LOT of money with the hopes of fixing the issue, he tried it for two months. It barely reduced the operating temps, and after removing the cylinder heads he found a worrying scale like build-up in the water jackets. It was enough to convince him to remove the coolant.