Your Mileage May Vary...Fuel Economy Thread

Discussion in 'Science and Technology' started by dmp, Sep 29, 2006.

  1. dmp
    Offline

    dmp Senior Member

    Joined:
    May 12, 2004
    Messages:
    13,088
    Thanks Received:
    741
    Trophy Points:
    48
    Location:
    Enterprise, Alabama
    Ratings:
    +741
    I'm transcribing this from a Road and Track Magazine...I thought some of y'all may enjoy the read. Know that i'm picking and choosing parts of the piece.

    Aero vs A/C

    The importance of aero has given rise to a good folk legend: You're better off, so goest the myth, running with your car's Air Conditioning (AC) on and the windows up, rather than invoking the added drage of what we used to call "440 a/c" (that is, 4 windows down, 40mph).
    The tradeoff is car-and velocity-sensitive, but my sources tell me that it's generally not beneficial at anything resembling legal speeds. Air conditioning can be as much as a 20-percent hit in fuel consumption. Unless heat and humidity call for it, you're better leaving the AC off and the windows rolled down (Purely as an aside, do young people wonder why we "roll down" a window?)

    There's a corollary to all this concerning a climate control's Defrost setting. This mode typically activiates the AC as a dehumidifier and is certianly essential in clearing the windshield and side windows. Once they're clear, though, you're better off switching the system from Defrost to Heat; otherwise you may be running the AC all winter long.


    Revs aren't Free - and alas, Neither is Speed
    It's only in racing - and with execptions even there- that "revs are free." In fact, entertaining though they may be - and sonorous though they may sound - revs pay a penalty in fuel consumption and in wear.

    Also, among the things under your control, one with a most profound effect on fuel consumption is your car's speed. Power requirements gro with the square of vehicle velocity (e.g., double the speed, quadruple the required power). And, obviously, power demand is directly related to fuel consumed.

    Whatever is an enthusiast to do?
    When I'm canyon running, corner strafing or, just for the fun of it, beating that fellow next to me across the intersection, I think of my earlier comment about 'Liquid entertainment'. And certainly we have the least expensive gasoline anywhere I'd want to live.
    On the other hand, a lot of my motoring is rather more mundane. And there's genuine satisfaction in performing it efficiently.


    WOT/Short-Shifting

    Remember Coah Grimbly's dictum about "driving with an egg under your foot"? Forget it. The most efficient way to reach cruising speed is wide-open-throttle (WOT) short shifting. That is, not only do revs cost money, but so does prolonged motoring in lower gear, when throttling and pumping losses are at their greatest.

    WOT/Short-shifting can save as much as 20 percent in city driving, worst to best case. In actual practice, rarely does traffic allow full WOT, but it's certianly fun - and efficient as well - to accelerate briskly through the lower gears to whatever the ambient speed happens to be.

    Once there, the appropriate choice of gear is one that offers modest RPM with relatively large (and constant!) throttle. Here, Coach Grimbly is vindicated. Dithering the accelerator is a pure waste of fuel, as is a slice-and-dice driving style. Read the traffic and go with the flow. Said one of my sources, "In fuel-economical mode, never request more power than is necessary to get to the next deceleration." There's a good enthusiast message here: Once up to speed, maintain it.

    And, of course, avoid last-instant braking that wastes both fuel and brake hardware. A word on hybrid braking; It's useful to 'shape the stop', that is, not to overwhelm the instantaneous capacity of regeneratvie braking. What's optimal is a relatively gentle initial pedal, followed by increased pressure as speed diminishes. Some hybrids have regen gauges that help in perfecting this technique.

    Last, a lot of this is manual-shift-oriented, but thoughtful mimicking with an automatic can yield benefits as well.

    I've got this neat fuel-saving gizmo!

    What of fuel gizmos? Briefly, save your money. Noted one of my sources, "The engine burns fuel with 99-percent efficiency. The inefficiencies are heat-induced, not related to fuel burn." Said another, "Such gizmos enhance the financial transfer from your pocket to the seller's."

    Automakers have tremendous incentive to improve their products. Anything with legitimate cost/benefit ratio - and thus, real advertising advantage - would be accepted in an instant.

    For example, driving aids, gizmos giving information that aguments fuel frugality, can be of real benefit. One example is tire-pressure monitoring. Another is a hybrid's regen meter to help the driver optimize braking techniques.
     
  2. glockmail
    Offline

    glockmail BANNED

    Joined:
    Aug 31, 2006
    Messages:
    7,700
    Thanks Received:
    433
    Trophy Points:
    83
    Location:
    The beautiful Yadkin Valley
    Ratings:
    +438
    Drove our just broken in Ford 500 from Winston-Salem (elevation 800) to our vacation home in the mountains (elevation 5000). On the way up I averaged 22.4 mpg (according to the dash display). For the 180 mile round trip I averaged 26.8. That means that I got 31.2 on the way down.

    The car has AWD and a CVT. Advertised highway milegae is 27 for this combo, vs 29 for the FWD 6 speed auto.
     
  3. dmp
    Offline

    dmp Senior Member

    Joined:
    May 12, 2004
    Messages:
    13,088
    Thanks Received:
    741
    Trophy Points:
    48
    Location:
    Enterprise, Alabama
    Ratings:
    +741
    My car is rated at 18 city/23 highway, although I never get better than 17 in town, and never better than 20 highway. Other RX8 owners are seeing mpg in the 10-15 range. :(
     
  4. misterblu
    Offline

    misterblu Active Member

    Joined:
    Sep 11, 2004
    Messages:
    611
    Thanks Received:
    64
    Trophy Points:
    28
    Ratings:
    +64
    That's because of the rotary turd under the hood. Oh, and because Mazda is personally out to get you. ;)


    :D
     
  5. dmp
    Offline

    dmp Senior Member

    Joined:
    May 12, 2004
    Messages:
    13,088
    Thanks Received:
    741
    Trophy Points:
    48
    Location:
    Enterprise, Alabama
    Ratings:
    +741
    And it's cuz Mazda is COMPLETELY full of shit when it comes to most engine-related specs. Check that - they are full of shit when it comes to two of the most important engine-related specs :)
     
  6. misterblu
    Offline

    misterblu Active Member

    Joined:
    Sep 11, 2004
    Messages:
    611
    Thanks Received:
    64
    Trophy Points:
    28
    Ratings:
    +64
    It's because you like cake. :thup:

    Mazda absolutely cannot stand the fact that you like cake.
     
  7. The ClayTaurus
    Offline

    The ClayTaurus Senior Member

    Joined:
    Sep 19, 2005
    Messages:
    7,062
    Thanks Received:
    332
    Trophy Points:
    48
    Ratings:
    +333
    Really? Seems to me I'm getting right AT their specs. The high spikes were 100% highway driving roadtrips (once there, once back), the rest is a mix, prolly 60-70 city and 30 highway on average.

    [​IMG]
     
  8. dmp
    Offline

    dmp Senior Member

    Joined:
    May 12, 2004
    Messages:
    13,088
    Thanks Received:
    741
    Trophy Points:
    48
    Location:
    Enterprise, Alabama
    Ratings:
    +741
    Have you had your car on the dyno? (to get AF readings?) My car runs...pretty rich.

    Can't complain TOO Much, because it does make pretty good power - for an RX8. W/ my intake and catback, I'm only about 10hp shy of what the car SHOULD have made, stock. :)

    :(
     
  9. Mr. P
    Offline

    Mr. P Senior Member

    Joined:
    Aug 5, 2004
    Messages:
    11,329
    Thanks Received:
    618
    Trophy Points:
    48
    Location:
    South of the Mason Dixon
    Ratings:
    +618
    I read a study a few weeks ago that concluded the advertised mpg was typically 10% higher than the real mpg. I think we all know whats on the sticker, for the most part, is BS anyway.
     
  10. The ClayTaurus
    Offline

    The ClayTaurus Senior Member

    Joined:
    Sep 19, 2005
    Messages:
    7,062
    Thanks Received:
    332
    Trophy Points:
    48
    Ratings:
    +333
    Alls I knows is I drives my car ands I gets the advertised mileage.
     

Share This Page