list of gas saving tips from best to worst

[Mighty Mira]

Thanks brucepick, I wasn't as confident as you about it (wasn't sure if pumping losses might change things), which is why I went the thought experiment route first. But the idea of "paying" to turn the engine was why I asked the question in the first place. Good explanation.

Another bonus of idling as opposed to having the car in gear (especially at high revs, like mine) is that the engine wear is reduced. Most of the wear occurs at the higher RPMs in other engines such as diesel generators, turbines etc. Just a few more RPM results in vastly reduced engine lifetimes.

There must be a sweet spot speed for P&G, assuming engine on, neutral. Since idle fuel burn rate is static wrt speed, the faster you go the better from that perspective. That will work fine until a point, where rolling resistance and air resistance increase to the point where more energy is wasted in moving air etc.

Note that there is also the pulse to consider. For that, we have to look at the engine map. Most of us probably have engines similar to the following engine map, which is a composite of EFI engines in 1995 (2 valve). In order to maximize efficiency during the pulse, we'd want to ensure that the engine was at least at 2000rpm and at about 3/4 of maximum load according to the graph (the line of the "island" represents equal efficiency (or Brake Specific Fuel Consumption, aka energy output versus, the each inner island having more efficiency than the next (read the link!). Hold on, I'll just compare:
2000 72%
3300 74%
3600-4500 70 - 100%



That's a lot higher than I thought. I was giving it 1/3-1/2 throttle, which I read somewhere on this site. I'll try and guesstimate what 75% of load is, since I'm not sure what the throttle required would be.

Anyway, I'll have a think about it some more later.