Gas efficiency and RPM
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This is a discussion on Gas efficiency and RPM within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; What is the best RPM to cruise at in order to maximize gas mileage?...

  1. #1
    Registered User younoleit's Avatar
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    Gas efficiency and RPM

    What is the best RPM to cruise at in order to maximize gas mileage?

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    personal experience... 2900-3100 is what i always cruise at gives me the best gas mileagefor the speeds i drive in which is around 120km/h. just try to stay outve boost

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    Registered User younoleit's Avatar
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    But the manual suggests a shift point of 45 mph, which is slightly less than 2k RPM I think.

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    The lower the better...
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    Registered User younoleit's Avatar
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    Quote Originally Posted by wrxdrvr View Post
    The lower the better...
    But past a certain point the engine can't make enough torque to be efficient, so what point is that?

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    The Member michaelwfox's Avatar
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    I shift at 2.5k and cruise on the highway at 65mph (speed limit here is 55 anyway lol). I'm averaging 24-27 mpg.

    Not that mpg even matters
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    Quote Originally Posted by younoleit View Post
    But past a certain point the engine can't make enough torque to be efficient, so what point is that?
    I didn't say to lug it, I suggested to keep the RPMs as low as practically possible to get where you are going, and you will get the best MPG that you can that way...
    '02 WRX 4EAT, 311,000KMs/194,500Miles, Sold. Best car I ever had. '09 STi stage 1, hope this one will be good too...

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    Registered User jimbo058's Avatar
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    I shift at 3,000, and then into 5th at 50mph unless going uphill, then I wait 'til 55 mph. I have been getting 28.5mpg with 50/50 city/hiway, so it seems to be working pretty well on my '09. I do romp on it several times a day, up on-ramps and to get by the occasional ****head, just to keep everything in working order !

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    Registered User poly_poly-man's Avatar
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    As low as possible is correct.

    There's basically a BSFC - an (almost) linear correlation between the BHP output of your engine and the fuel consumption, for certain ranges (think CL). To go a certain speed, you need a certain amount of torque. Since torque * rpm * (arbitrary constant) = HP, the lower your RPM for that particular torque, the better.

    The situation only gets worse - higher speeds get exponentially worse in terms of wind drag (increasing torque required), and higher engine speeds could start dragging you into OL fueling, and could definitely target richer cells on your fueling map.

    Basically, keep it below 70 in 5th gear (with the ratios I'm used to), and if the next highest gear will let you sit around ~2k or above, shift.
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    Registered User teflon_jones's Avatar
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    How hard you're pressing the gas matter more than your RPM. Hammering on the pedal at 2k RPM will burn a lot more fuel than coasting at 5k RPM.

    I've done a lot of comparisons in different cars and regardless of the car/engine type RPM matters much less than how hard you hit the throttle.

    Along the same lines, turbos burn gas much more quickly at high RPM than naturally aspirated motors, so staying out of boost also saves gas. You can stay out of boost by staying at low RPM or by simply not hitting the gas hard.

    And of course the faster the engine turns the more gas it burns versus lower RPM, but throttle pressure plays much more into the mileage as stated above.
    Last edited by teflon_jones; 06-21-2012 at 03:45 PM.
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    I shift just above 2k around town. I average 24+ mpg city all day. On the freeway, I suggest keeping it right at the speed limit, if not lower if you want the best mpg, that's pretty much common sense.

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    Registered User younoleit's Avatar
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    Thank you everyone for the input.

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    Subaru Newb MainFrame's Avatar
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    Quote Originally Posted by teflon_jones View Post
    How hard you're pressing the gas matter more than your RPM. Hammering on the pedal at 2k RPM will burn a lot more fuel than coasting at 5k RPM.


    ^this.. load and throttle opening angle are far greater contributing factors to mpg than rpm.

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    You are better off (for higher MPG) in a gear that makes the engine work a bit at a lower RPM (not lugging the engine), than higher RPMs, almost always...
    '02 WRX 4EAT, 311,000KMs/194,500Miles, Sold. Best car I ever had. '09 STi stage 1, hope this one will be good too...

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    Registered User poly_poly-man's Avatar
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    Quote Originally Posted by MainFrame View Post
    ^this.. load and throttle opening angle are far greater contributing factors to mpg than rpm.
    load clearly - I mean, that's just a few multiplications away from being injector duty cycle :P

    And no, is the cruising type situation I'm talking about (same speed, same conditions, going one constant speed, or for a particular amount of torque required), the 2k situation will, 100% of the time, be better on gas than the 5k situation, even if you're talking a steep uphill which requires WOT at 2k.

    Now acceleration is a different matter altogether.
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