I appreciate this is subject where it's easy to get tangled and every board has at least one of these threads.
The reason I chose ported was that I did not want full vacuum at idle. I have experimented with that in my other car in the past, and found that it worked well, except in stop and go traffic where it wanted to keep revs up a little, unless I blipped throttle. Why, I don't know, and I understand it could well have been a side effect from some other issue.
Had a chance to drive a little yesterday. Warmed up real good with high speed highway driving and did some fifth gear acceleration tests. With full throttle, heavy load, relatively low rpm acceleration test (which should be the worst case for detonation) I hear some pinging, not much, but it's there. So, I have little too much advance there, either vacuum or centrifugal. In smaller gear acceleration I don't hear any detonation.
You say that ported vacuum keeps rising with throttle opening and manifold goes down. Intuitively that makes sense, and will be easy enough to test if going to manifold vacuum helps in my case.
However, I found someone had datalogged ported and manifold against each other and throttle opening, showing they are the same outside small throttle opening.
It may be that I still need to adjust centrifugal. And still may be that direct manifold would work better with lower temps at idle. And direct manifold might not have the erratic idle behavior with this engine. I'll probably need to get that IR temp gun as well to make sense of it all for myself.
Here's the datalog I found at www.gofastforless.com. I don't post this to argue your experience, but for information only, as someone has gone to trouble of measuring it. Depending where the ported vacuum source in the carb venturi resides, there may be differences between carbs?
