@Isaac Zachary
You make a lot of good points, I agree with basically everything you've said. Like you've mentioned, diesels don't have a throttle plate and besides the higher compression the engine is effectively the same as a gasser, but they achieve higher efficiency numbers (fuel to mechanical movement).
I've done some thinking on how to make a gas engine run like a diesel with no throttle. Pretty much best I've came up with was direct injection that injects near TDC and continues to pump fuel in for as long of the stroke to reduce the instant burn effect to keep pressures and heat down. Maybe something like a staged injector where it injects as like a pulse and have 2-4 of them per cylinder. This concept of mine would be compression ignition btw, no spark plug since you can't keep the ideal air fuel ratio with the throttle wide open unless you go the route of a hit and miss engine which probably wouldn't be too accepted as a design for a car engine. I'm no engineer but I do like to know how things work and generally can work out things in theory pretty well. I don't think I'll be building a compression ignition gas engine any time soon. Mazda has though.
https://www.roadandtrack.com/new-car...soline-engine/
Another interesting concept I've had since I got a prius with the atkinson cycle engine, what if the engine was sized to the load needed to maintain speed at say 70mph or whatever the max speed the vehicle would be traveling at, and run it at low compression with the throttle wide open. For take off, it uses higher compression for the more needed power (maybe a super charger too?). Clearly at lower speeds it wouldn't be able to work at perfect efficiency, but I'd think the effect would be pretty huge having a smaller engine running closer to ideal conditions more of the time. VVTi exists, so the prius engine design should work for that concept I'd think with the vvti on the intake valve adjusting the effective compression ratio on the fly.
Couple big questions with that concept is compression ratio efficiency vs pump losses that are reduced with the wide open throttle plate. I suspect the overall effect is nearly a wash or a company would already do something similar for a "normal" car since the concept isn't that complex and the tech already exists to pull it off.
A while back I had the idea of why not have 2 engines in a car, one for steady speed with a little overhead for small hills and such so it runs basically wide open all the time and the second engine acts sort of like the prius traction battery, it assists with take off and is the real "power" for the car to get up to speed. Clearly it would need some sort of clutch system between the two engines. Since I've seen the prius design, I wonder if the CVT design could be designed with 2 engines fairly easily. That setup would probably require the electric motors and a similar setup to the prius except doubled up and somehow tied together. I haven't thought too much on this design besides the basic clutch concept.
@mpgmike
The effective amount of air that gets into the engine is still the same even with the smaller carb for the same power output level. Air in dictates how much fuel is needed on a gas engine. The pump losses if measurable could be done with a MAP sensor and a data logger. Go say 55mph on a stretch of road and average out the vacuum reading, then repeat the same test with an extreme restricted intake to see if it makes any difference. If the air into the engine is the same, the vacuum readings should be the same for the average. I'd be interested in seeing something like this done, clearly max hp is massively effected, but cruising speeds isn't done at max hp. In my head, the peak vacuum would increase since it's harder to move the air, but the average is what an EFI computer uses to calculate the fuel charge needed to be injected to be at the right air fuel ratio.
The more I think about this, the more i think Isaac Zachary is right that the intake restriction is more or less a moot point when dealing with a gas engine. To get into HVAC systems, there's a long small copper pipe that's used to create a restriction for the liquid refrigerant to be released into the evaporator at a fixed rate. There's a different design that you can use effectively a needle valve. Both systems operate the same way if the needle valve is adjusted for the same flow. The long tube would be a highly restricted intake vs the needle valve would be the throttle plate. If there's a difference in efficiency, it's unmeasurable in ac systems from my understanding and that's with a liquid.