AJC..
Same here i had never problem with my own made cylinderheads with flat contrapiston and some of them has squishband when the engines ran well without to be hotter.. As i wrote before in early post, there are possible not enough cooling fins in his (Micropuller) cylinderhead since it is a car engine. And if he has used too much MEKP in fuel, it will run hotter.

Jens Eirik