Not necessarily. It all depends on how quickly you want to accelerate. If you're in traffic and acceleration rates are pretty low, you'll be better of consumption-wise shifting at low rpm. The quicker you want to accelerate, the higher your shift points should be.

No, the key to maximizing fuel economy for a given acceleration rate is to maintain a wider throttle opening and short-shift. Small throttle openings in a lower gear will give you worse fuel economy. That said, taken to the extreme of keeping it floored and shifting at 2000rpm is not a good idea, as you'll usually be on a part of the map where the mixture is enriched.

Acceleration rates will dictate optimum shift points. And obviously driveability is a factor.
One tankful does not give enough data anyway! A valid test would require a lot of runs and ensuring exactly the same acceleration rates. But if your acceleration rates required a near fully open throttle at 2000-2500, then you could easily be going to a richer mixture which would not be good for fuel economy.

Driving for efficiency, I will shift such that I can maintain about 50% throttle. This works well and gives me ~20-24mpg in town. If you stay in lower gears longer and shift later while maintaining a much smaller throttle opening, say 25%, for the same acceleration rates, I would bet a 6-pack you will get worse fuel mileage.

 

Finally...I see where the breakdown is I just accelerate too much and to do that at lower rpms requires more fuel Just the way I drive compared to others

I never bought an S to accelerate at yuppie-rates of speed. Throughout this convo my mindset was always a static rate of acceleration that I am used to doing...didn't even consider that people might accelerate the S at say Prius levels.

I digress

 

Regarding the efficiency map, you have to understand that efficiency in the sense of maximum power per unit of fuel consumed (or minimum fuel consumed per power produced) is NOT the same thing as fuel efficiency. You will get maximum fuel efficiency by maintaining a low speed where the power level is lower, even though that puts you at a "bad" part of the engine efficiency map. It is better for fuel efficiency to cruise at 45mph where you only need ~11hp (8kW) to maintain speed, than to cruise at 75mph where you need ~26hp (20kW). Even though if we go by the map above you would be consuming more fuel per power produced at the lower level (~450 gal/kW-hr at 45mph, ~300 gal/kW-hr at 75).

 

I never said constant rate of speed. It could be for a given acceleration too. Either way we're talking about equal power. I think taller gears may have a problem if you need enough throttle that the ECU goes to open loop. That may cause it to run richer which would hurt fuel economy. So, the question is does "cruising" include that? In my opinion it wouldn't.

 

"cruise" has totally fubar'd this convo

 

Whether we're talking about same-speed cruising or same rate of acceleration, in both cases we are talking about the same power level. It's just that for cruise the power level is a lot lower.

If we look at the point referenced in drpizza's map above, 40kW (53.6hp) output, which would be an acceleration rate of ~.25g at 30mph in an S2000, the map is telling us that 2000rpm is the optimum place to be for fuel efficiency for that engine. 1700rpm would be as bad as 3000rpm for fuel efficiency at that power setting.

For 75mph cruise, ~20kW (26hp) required, optimum rpm for fuel efficiency is 1300rpm for that engine.

Higher power setting => higher rpm for max efficiency.

Of course the S2000's efficiency map will be different, skewed higher in rpm by ~2x.

 

Agreed I read the OP, saw "don't want to be cruising at an unreasonable RPM" and thought "conservative shifting" applied to when you're done accelerating and want to get into right gear to save gas. How quickly you accelerate is all up to you. When there's fewer cars around I rev to 4 or 5. But I do have to drive the S in Prius mode a lot, especially in LA traffic. So I go into hypermiler mindset because you might as well try to make the commute interesting.

But in that case if you shift at 4-5K, do you hold the RPMs that high at steady speeds in town?

Also thanks ZDan on the analysis of the graph. The chart was just meant for a rando gasoline motor as previously mentioned so the numbers dont' directly apply

Agree that if you accelerate way too slow you try to get too little power output, at the bottom left of the chart, and the "acceleration per gallon" is actually worse when you accelerate TOO slow. But I think most of us are just pretty much keeping pace with traffic.