+1.....Auto will be the best for fuel effeciency.
C.

 

So if the throttle is only barely pressed, only a little air can possibly be sucked in by the engine. If it opens all the way, it can suck in full capacity. Otherwise a vaccuum is maintained/built-up ahead of the throttle body. This tells me that the engine takes in more air w/ the throttle open, and therefore more fuel. I need more details of how that's wrong before my brain will accept it, please

This has been my understanding since way back when I had two cycle R/C cars with servo-controlled carburator

 

You're right, the engine takes in more fuel with the throttle open, but only as an indirect result. If you consider it at an individual cylinder level the air charge, fuel charge and work performed are relatively constant (all engine management subtelties aside) for any given two-rev cycle, regardless of the throttle opening or the RPM of the engine at the time. Opening the throttle just "releases the hounds" and lets the engine spool up it's natural chain reaction towards the redline.
It may seem like semantics, but it comes back to the fact that at a steady cruise, fuel consumption will be proportional to RPM, all other factors being equal. I'm not disagreeing with anything in the post quoted above, I'm just following up from when I shot my mouth (fingertips) off a few posts ago when terms like "doing more work" and "acceleration potential" were being used to explain changes in fuel consumption.

 

Well obviously, I think most of us are right when it's only what we meant that's taken into consideration and not extensions beyond

I was using those terms to explain how it is possible that, in a throttle-closed situation, you could be at a high RPM at the engine and yet consume very little fuel because in essense you are letting the car's momentum keep the flywheel turning fast, not asking the engine to do it. And, I was extending that to gentle acceleration, whereby you don't see immediate drastic drops in MPG just because of higher revs (outside of extremes).

Obviously long-term cruising at high rpms will burn more fuel than low rpms.

 

It's called being in violent agreement.

 

^^^ Awww...they kissed and made up! Look at that! haha. Glad we can all be civil after all.

 

get a civic and keep your g garaged, that way you'll save gas.
Ok?

 

Hehe. Hate to bug ya but what is your explanation for how we burn much more fuel going up a hill (maintaining speed) while the RPMs remain constant (since they are mechanically forced to spin at the same ratio to the rear wheels and we are maintaining speed)?

 

As I said, RPM isn't the only factor in consumption, but it's the primary one, especially in a level, constant cruise which was the scenario I originally posted about. Active engine management will cause more fuel to be burned in the "transition" to increased RPM - and an uphill grade, rolling resistance or wind resistance can simulate that transition. But working against that resistance in a higher gear will burn less than shifting down and increasing the RPM's to maintain the same speed. Obviously there's limits as to how low you will lug a motor in a given situation.

Now it's your turn, how exactly does that "acceleration potential" theory work?