[Barty]

Originally Posted by BuickCFI

more vacuum pressure, i didn't put that in there. the engine is working harder to get air so the vacuum goes up. at full throttle it is ambient because there is no vacuum pressure

You need to stick to either referring to it as pressure or vacuum. Personally, I find it easier just to refer to everything in terms of pressure and pressure differential when talking about engine load. What we are referring to as vacuum is really a difference between atmospheric pressure and the lower pressure in the manifold. In this way, it also makes it easier to understand what is really going on with a turbocharger/supercharger. Both are merely devices that either work to keep manifold pressure equal to what it would approximately be at sea level or to provide pressure higher than ambient. Generally, most aircraft turbochargers fall into the former category.

But there is no "vacuum pressure."