Vacuum advance information and myths

Basically yes.
The initial timing of a pre-emisions or non-CAP engine provides good power, and idles smooth and strong.
The same engine with a CAP package used much less initial advance. The mechanical advance in the distributor makes up for that above idle rpm.

Pick an engine in the mid-60s that had both a non-emissions and an emissions reduction package on it and compare the inital timing and rpm. Then look at the mechanical advance of in the distributor of each. I've posted a number of these in graph form. Here's one

View attachment 1716030499

CAP vs nonCAP 273 4 bbl here.


Love to see them.
Last time we thought we found one it turned out to be ported. That was a 1966.
I'll take a pic in a few and post it. The tag fell off years ago but I'll get pics of the numbers it has. I don't have the car anymore but still have the carb and converted it to elect choke. It was on my 66 300 440 tnt, dual point dist. Might have dist also but sold my dist machine 10 years ago so I won't be able to compare actual mech curves like I would like.