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Now, consider that the exhaust manifold pressure is, for all practical purposes, the same as atmospheric pressure. This means that we can, for all practical purposes, use intake manifold vacuum for this DCD discussion (as well as lean-burn), as intake manifold vacuum is the difference between atmospheric and intake manifold atmospheric pressures. (Please note that I am not addressing exhaust backpressure, take any discussions about exhaust backpressure elsewhere, and let's not muddy up this thread more than it already is.)
Now, it should be obvious that if we raise intake manifold vacuum, we are raising the amount of pump work that the engine is consuming. Similarly, lowering intake manifold vacuum will lower this amount of pumping work. Right?
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