Supposedly the most fuel efficient way to run a ICE engine is at full throttle. You may recall that BMW's recommendation for maximum fuel economy for the 1980s 528e was 3/4 throttle acceleration and very early shifts in every gear.
So if you could get a V8 to run off a small carburetor you'd have to run it at full throttle or near full throttle all the time anyway, so it might get quite good mileage. No performance to speak of, but good mileage!
Yes, at part-throttle an ICE's pumping losses are high, and so efficiency is low. And therefore, contrary to what we were taught all those years ago, maintaining a steady speed is not best for efficiency.
Hypermilers address this with a technique called "pulse and glide" - use close to wide-open-throttle to quickly hit the desired speed, coast down to somewhat slower, and repeat.
I tried it some years ago, and got very good mileage over the course of that short test. (This was per a ScanGauge.) This was early on a weekend morning, and so I wasn't interfering with other traffic. The downsides make it impractical in most circumstances:
- Rather than driving at a constant speed, you're speeding up and slowing down constantly, which messes with traffic.
- To maintain an average speed equal to the posted limit, you have to be above the limit about half the time. Try explaining to photo radar that your average speed was legal.
But on a backroad, it would work well.
Relatedly, Toyota calculated back in the '70s that lowest fuel consumption occurred at about 50% of redline. This seemed to be borne out by their 4-speed Corollas getting better mileage than the 5-speeds.
I wonder if this tied in with a larger throttle opening?
Audi, and perhaps others, gave their US-export cars a shorter final drive to increase the RPM at the (legal) speed limit of 55 MPH.
