My builder told me that too, for a 292/292/108 cam, into a 360.
and he was right in as much as the 69 dual-diaphragm booster was lazy. But before I threw in the towel, I bolted on a booster off a late 70s F-body.
The idle vacuum of the 292 cam was pretty low, but the F-body booster worked pretty good. It only took a blip on the throttle to charge it up. By the time I had backed out of the carport, and idled off the yard, it was fully charged.
My car is a stick, so I installed a Line-loc to be a hill-holder, so I never have to pay attention to the idle vacuum anymore, while stopped at a light.
Because it's a stick, and I downshift when coming to a stop, the intake vacuum is always high enough.
The only time that the booster gets lazy, is when I'm idling around the parking lot at 500/550 rpm in first gear..... but since it's under 4mph, I don't even notice.
And finally, by 900rpm the vacuum is sufficient to charge the booster.,
So, with this knowledge, I know I can go up another size in cams at least before it becomes a thing.
The point is this, you may not know that you need one until you roadtest your combo with whatever you got. But I will say that the dual-diaphragm I had was lazy. Since it is field-rebuildable, I took it apart ...... and there was nothing wrong with it. So I mean, your results may vary; but I don't recommend one of those. I found out, years later, that others had had the same experience.
