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Originally Posted by brick
My shift points are in the range of 2000RPM under moderate (50-65%) load. While cruising is the most efficient state for the car, it is impossible to make up for a very inefficient (in my case 10-20mpg) start with a few hundred extra feet of cruising. Remember that you can't un-burn that fuel, only average it out slowly.
As far as pumping losses are concerned, I think that's really the wrong way to look at it. Going WOT for a few seconds may be a more efficient way to produce power, but that doesn't mean that you are using the extra power efficiently. In addition to paying for the kinetic energy gained, you also have to pay for significantly increased drivetrain losses if you end up at high RPM (a factor especially for automatic and CVT-equipped cars) and slightly more aero drag due to slightly more distance travelled at high speed.
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Ending up at a higher RPM is a valid point, which is why I mentioned the technique specifically for manual transmisisons/shifting at the lowest RPMs possible. Combined with other mitigating factors, your acceleration strategy is close to optimal.
It's also true that average speed will be slightly higher, leading to slightly more drag. If I wanted to nitpick I suppose you could compare accelerating at a slower rate to a slightly
faster top speed, so that you'd end up at the same overall average speed, for the sake of comparison
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Finally, many vehicles run rich at WOT under open-loop fuel management in order to protect the engine from pinging and detonation, which is akin to dumping fuel directly out your tailpipe. So I don't think there's anything to be gained except thrills, engine wear, and two seconds off of your trip time.
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These are some good points, which would mean the optimum efficiency in the engine would be found at the widest throttle position before these mitigating factors (fuel mixture, etc) come into effect, probably about 2/3rd throttle at 2000rpm, which is generally where I'll accelerate.
The only other case where I'd say it's more efficient overall to accelerate as fast as possible is if accelerating more slowly would impede traffic behind me and reduce their fuel efficiency. For example, if I am the only car in my lane stopped at a traffic light that has just turned green, with traffic at full-speed approaching me, acclerating very rapidly will mean that all those cars behind me can simply maintain their speed. Accelerating at a slower rate, would force them to slow down more, then re-accelerate -- a huge amount of fuel when multiplied across several larger vehicles, though I personally don't see any of those savings, it is a reduction in overall emissions.