Ask the Best and Brightest: "Is the Efficiency of Slow Acceleration Just a Myth?"
"What is more fuel efficient for automatic cars, accelerating quickly or slowly? And what is generally peak torque for typical passanger cars and trucks? For manuals, quick and smooth acceleration is most efficient. I would expect that the same is true for modern automatics, but don’t know for sure. With my own automatic trans car, I notice no difference between the two, maybe a slight improvement with faster acceleration. In the past, a study was done comparing slow braking and acceleration with fast braking and acceleration, but they didn’t investigate fast acceleration with light braking. I’ve been accelerating quickly (but keeping RPM below 3500 where I suspect efficiency drops off) and adjusting my speed mostly with the accelerator (easing off earlier to provide a little extra safe following distance and keeping near the speedlimit to time traffic lights). I get pretty good gas mileage, between 26 and 30 MPG (mostly sub-urban highway driving during rush hour). Before I started accelerating more quickly I got about 26-27 pretty consistantly. Is the efficiency of slow acceleration just a myth?"
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When you drive around town, I always try to remember that what burns fuel is braking. If you think about it in terms of energy conservation, the only energy wasters (ie energy not doing useful work) are aerodinamic loses, rolling resistance and brakes. Aerodinamic you can only make better by driving slower, and around town it does not matter that much. Rolling resistance you can improve by using better tires and inflating them properly and also by making sure your car is well mantained. So it comes down to brakes. If you drive avoiding the brake pedal, your city fuel efficiency will improve a lot. You'll also be driving safely.
"Some people have mentioned the fuel mixture running rich at WOT, which makes me wonder: doesn’t a rich fuel mixture destroy the catalytic converter? Needing a new one of those will get rid of your fuel savings pretty quick." Maybe I should mention that my check engine light has been on for a year. I guess it could be the cat. No point in getting it examined though.
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