Fuel Economy and RPMs and VEs

[KendallF]

Is it true that for a given car and gearing, you'll always get better gas mileage by lowering the RPMs?

I've got a suspicion that this is not true, but I can't pin it down.

Is fuel economy directly related to Volumetric Efficiency? In other words, should I be tuning my car/choosing components so that cruise speed on the highway is at peak torque/peak VE/something like that? Or is it indeed just a matter of spinning the motor a little less?

Peak WOT VE usually occurs around the torque peak. But..to run at a constant cruise speed at higher RPM requires less throttle opening. I suspect that, for at least midrange off-idle to torque peak RPM, VE gets worse as the throttle is closed and the motor must pull turbulent air around the throttle blade. Also pumping losses and rotational losses are proportionate to RPM (or RPM^2).



So..I'd conclude from these factors that the lower the RPM and the wider open the throttle the better for cruise efficiency, until you get it so low that the VE falls off due to the intake, cam, and head design. Does that make sense to anyone else?