This is a subject I had heard of before, but it never really clicked for me until I came across a forum post talking about it when I was looking for something else.
Engine quench is the distance between the piston and the cylinder head.
The post I referenced in the show that got me started on thinking about engine quench is:
The one I found about the coffee can is here:
Here is a picture of an open chamber head:
Here is a closed chamber head:
Here is a Google search link for images of a 426 Hemi cylinder head. Notice no way to get quench:
And by contrast, the gen 3 Hemi. Notice the quench pads that give the combustion chamber an oval shape. Sure, not a “real” Hemi, but they give a great benefit.