Heat is good (to a point) for an ABC engine while breaking it in. Heat is NOT good during break-in of a ringed engine. What you are trying to do is 'seat' the ring. This requires a lot of lube and as little heat as possible at first to do it right. I typically will run a ringed engine VERY rich for the first ~10 three minute runs letting it cool completely between runs. Gradually over the next ~10 three minute runs lean it out to just richer than full lean, letting it cool completely between runs. Yea, this takes a while, but it will make the engine last a LONG time and develop FULL power!

BTW, in the event you ever wish to use an old engine (pre ABC) it will require the same break-in as a ringed engine.