i believe it has to do with the surface area and the actual dome itself, because of the castings used for the pistons
it’s hard to explain, i have an analogy but i don’t feel like typing it lol
Well I guess with typical B-series builders I see how that could work since there are so many different heads and pistons. People are always mix-matching heads and pistons to the point where the extra bore doesn’t increase CR just because the dome isn’t ideal for the head they’re using.
That’s the only way I can see it being possible. But all things the same, bigger bore = higher cr.