Floog, so you bubbled the paint on the UPPER cowl? I didn't think the exhaust headers were up that high. Or did you mean the upper part of the LOWER cowl?
I ran my engine several times on the ground at WOT to check static rpm after fussing with prop pitch (ground adj.) at around 5200-5300, but did not keep it at this hi speed for very long. That's probably why I got no paint blisters.

Did you have to repaint the cowl, or just a small patch?