I'm specifically referring to the loss due to the pistons pulling air through a mostly closed throttle while cruising at highway speeds in a gasoline engine.
To give an example, I've always wondered why this wouldn't be more economical fuel-wise:
Add another gear to the gearbox, say a sixth gear to a 5-speed car. This gear would be useless for accelerating whatsoever; it would be such a high ratio that at 65 MPH, wide-open throttle, it would hold the vehicle at a steady pace or only slightly accelerate. This would reduce much of the pumping losses from making the pistons suck through a nearly closed throttle, and would seemingly allow for better fuel economy, due in part from both 1) lower RPM so less friction loss and 2) less pumping loss.
I am aware other things may need to accompany this; for example WOT in 6th gear should not richen the mixture as WOT does normally, etc., so let's say the car was produced from the factory with the computer and associated electronics accommodating the fuel-gear.
However, this has never been implemented. Is it just not efficient? If not, why not? Or would it be an irritation to consumers that expect a more responsive car, requiring a shift to accelerate? Too expensive to add the gear, or just never been tried?