Originally posted by: Zenmervolt
Originally posted by: miri
Originally posted by: audi
outstanding tips :|
You would be surprise at the number of people that shift at 4000-5000rpm and cruise at over 3000 and wonder why they get bad gas mileage.
Short-shifting with small throttle openings vastly increases pumping losses. The best strategy for fuel mileage is to short shift with large throttle openings. That is to say, you will get better mileage from flooring the accelerator and shifting at 2500 RPM than you will by easing into the accelerator and shifting at 2500 RPM.
Full throttle acceleration and shifting near redline yields approximately the same mileage as easing onto the accelerator and short-shifting.
Most people wonder why this is, but it's simple. The engine has to work incredibly hard to suck in air past the highly restrictive throttle butterfly. This energy that is wasted in trying to get air past an almost-closed throttle butterfly more than offsets the lesser fuel delivery rate of the injectors at low RPM. This is also the main reason why Diesels are so much more efficient than gasoline engines, a diesel has no throttle butterfly to restrict airflow into the engine. (Diesel fuel also has a marginally higher per-unit-volume energy content, but the largest factor in diesel efficiency is the engine's lack of pumping losses compared to an equivalent gasoline engine.)
Furthermore, most vehicles get peak fuel mileage between 35 and 40 mph. My big Lincoln with a 280 hp V8 gets 34 mpg at a steady 35 mph (it's in overdrive by that point, very low gearing). It gets only 27 mpg highway. If you're not stopping much but instead just driving at a constant, albeit low, speed, then you aren't going to suffer drastic mileage losses. The reason "city" mileage is lower is because of constant starting and stopping, not because of the speeds the car achieves.
ZV