My home inspection of Speedmaster heads

As has been mentioned...... these are copies of Ede heads.
The plug holes are done that way in the RPM heads, and since that’s the head they copied...... the threads are the same in the SM heads.

My guess is over 95% of the sets in use have not had anything done to the plug holes.
Yes, at the least or at the most? for most myself included it is just a finish detail, like chamfering edges tidying things up, of minimal performance benefit other than theoretically maybe relating to hot spots? but I’d think at the level PBR is at like he said every little bit helps. I only noticed the difference in finish inspecting the TF’s. Lots of attention to detail on these.