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Car fuel efficiency/throttle position?

  1. Apr 16, 2009 #1


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    Which method of driving results in higher fuel efficiency? a) accelerating with the throttle only slightly open and delaying upshifting until high engine RPM or b) accelerating with the throttle full open (pedal to the metal) but at low engine RPM/upshifting early?
  2. jcsd
  3. Apr 16, 2009 #2
    The best engine efficiency based on BSFC (brake specific fuel consumption) maps is to run at about 35% of redline RPM and about 80% of maxumum torque (wide open throttle). I typically shift up (manual transmission) at about 2000 to 2200 RPM unless I need more acceleration. In the city, where you usually need no more than about 10 HP, I keep the RPM between 1500 and 2000 RPM, and usually get into 5th gear about 30 mph. The manual transmission is about 96% efficient, except in 4th gear which is about 98%. An automatic is typically only about 85% efficient,
  4. Apr 16, 2009 #3


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    The actual numbers are Dependant on the size of the engine.
    Basically go as slow as possible in as high a gear as possible
  5. Apr 17, 2009 #4

    Ranger Mike

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    regardless of the induction system, carb, direct port , throttle body..ifin ya want to save MPG, drive it like you got an egg between the go pedal and yer foot!
    better yet, switch to synthetic oil once the engine is broke in,
    keep the tires inflated , max end of the recommended PSI, on 1990 and newer cars keep all windows UP..the old myth of no air conditioner and open the windows is not applicable to todays cars..max MPG requires mucho AERO and windows up gives max MPG, opening a window on new models severley impacts MPG
    replace spark plugs after 30000 miles
    go to Iridium spark plugs.. $ 8 each but require 5000 volts less to light
    check and clean air filter regularly
    light is better so take all those old empties out of the car
    want to experiment a little
    keep the car waxed..slick is better..ok maybe yields .1 more mpg but hey..it all helps
  6. Apr 18, 2009 #5


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    No. Driving in too high a gear will require more fuel than driving in a lower gear around the BSFC peak.

    Correct. If that means changing down a gear and using less throttle, do it.
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