I should probably have noted that I'm using HEMI here in the colloquial manner, referring to anything using hemispherical-style chambers, kind of like how most facial tissue gets called "kleenex" despite both being brands from specific companies.
I was referring to Ford's pursuit of using HEMI chambers too, which started with the 427 SOHC, which had true hemispherical chambers:
View attachment 123055
and the Can-am and competition versions of the BOSS 429 also had fully hemispherical chambers, but they added a quench area on each side of the chamber for the street version, due to the reasons I mentioned, which they experienced with the 427 SOHC, but Chrysler also experienced with the 426:
View attachment 123056
Toyota used the area around the chamber as quench:
View attachment 123058
but also experimented with quench areas like Ford did:
View attachment 123059
Nissan did similar:
View attachment 123060