Thinking of swapping mufflers but got a question pertaining to my 340

YR, I think Cranky's post is correct on the H AC, but differ's because of the engine is or has a pulse and the HVAC system does not.

In exhaust, we're moving hot gasses and we would want to retain some heat as so not drop velocity and allow cooling gasses to tumble. And the same with to large of a pipe.