That's in a theoretical sense correct, if you cranked an engine 4000 times and then 3000 times the volume of air pumped by the engine 4000 times would be more, assuming that the manifold pressure were at ambient.

Changing the manifold pressure causes the cylinders to be filled with a proper A/F ratio at a pressure below ambient, and containing less fuel.

Opening the throttle more at 3000 rpm could result in pumping more air than a more closed throttle at 4000 rpm.

which is why i said it's hard to do without a vacuum gauge.

As you get the manifold pressure closer to ambient, you burn more fuel, and get worse mileage. ( unless you have a turbo {in some cases} )

A lower revving engine has less oilpressure, i'll take my chances at 4k with 50 lbs vs 35psi at 3k.

Theoretically it is correct. Quote:And hence the answer. The harder working engine may be tuned to be more efficient, thus (theoretically) uses less fuel.

In reality, it almost always makes more economy at lower RPM because our engines are larger than they need to be. Even the A12 is bigger than needed to sustain 100kph.