...with the caveat that there are some slightly conflicting opinions.
- TEST of various fuel economy tips by Edmunds.com:
If you slowed your 0-to-60-mph acceleration time down from your current 10 seconds to a more normal city pace of 15 seconds, you'll feel the savings immediately.
Up to 37 percent savings, average savings of 31 percent
The method, summarized below, is found HERE:
- Cycle 15 times from 0-75mph at 3/4 throttle, braking hard in between, total: 55 miles
- Cycle 15 times from 0-75mph at 1/4 throttle, braking lightly in between, total: 55 miles
- Cycle 25 times from 0-65mph at 3/4 throttle, braking hard in between, total: 25 miles
- Cycle 25 times from 0-60mph at 1/4 throttle, braking lightly in between, total: 25 miles
Now, I really, really, really wish they had isolated their variables. I don't know why they considered it necessary to vary the braking style and top speed in these cycles. There's at least some indication here, though, that accelerating faster decreases fuel economy. I consider "flooring it" to be a subset of "accelerating faster."
- THIS 2001 paper from Energy and Environmental Analysis, Inc., on which the US Dept. of Energy bases it's fuel economy recommendations HERE tested 17 cars and the effects of "aggressive driving cycles" (faster acceleration/deceleration, different maximum speeds, etc.) and concluded that:
Very powerful cars exhibit negligible fuel economy penalties, while an average car is likely to experience a penalty of about six percent [at lower speeds]. At higher speeds, typical of urban expressway driving, however, the fuel economy penalty of aggressive driving is both significant in magnitude and more consistent across all cars. The average car is likely to experience a penalty of 33 percent, with more powerful cars experiencing a somewhat lower penalty of about 28 percent.
So... there was a loss due to aggressive driving, but it's not that high and doesn't square with what Edmunds.com said, either (Edmunds.com had much higher loss reports). This paper also didn't isolate all variables, but went with a "driving style."
- THIS paper by Dr. van der Voort, looking to design a dashboard device to provide driver feedback in order to increase fuel economy. HERE is a layman's writeup about his summary from The New York Times.
From The Times' article:
"People were shifting too late from first to second, and from second to third," Dr. van der Voort said. People saved the most gasoline when they pushed down on the accelerator briskly and then shifted quickly, keeping the revolutions per minute low -- not by accelerating very gently.
And from van der Voort's actual paper:
Further analysis revealed that drivers without support [the dashboard display instructing them on optimum driving habits] shifted significantly more times too late from 1st to 2nd gear and from 2nd to 3rd gear than drivers who received support (and drove more fuel-efficiently). No significant differences between the groups were found with regard to shifting from 3rd to 4th gear.
So, we can see that late shifting results in a decrease in fuel economy. In automatic transmission cars, "flooring it" will result in the car being kept in as low of a gear as possible, thus bypassing the optimum shift point for maximum fuel economy.
I wish the sources had been as simple as "faster acceleration yields lower fuel economy," but it wasn't quite that simple. For instance, I was quite surprised to find that more powerful cars did not suffer as badly from aggressive acceleration in the second source! The overall convergence of the sources is that faster acceleration (or at the very least, not shifting as speed increases) yields lower fuel economies.
I really wanted to answer this in terms of power curves and torque, but could not get my head around enough to put the facts together. I think the real why of this answer would lie in keeping the power output of the transmission (which is the torque of the engine "filtered" through your gear box) matched for the speed of the vehicle. My attempts at digging there tended to come up primarily with "hot rod" types of sites that are primarily focused on maximizing acceleration, not fuel economy.