Gas Mileage on a Run

M Body General Discussion

  1. The Director

    The Director Active Member

    Messages:
    33
    Likes Received:
    12
    Joined:
    Oct 13, 2019
    Location:
    New Jersey
    So, a few days back, I took a 131.15 mile round trip. (I know, absurdly precise, but it was imperative for the math behind this.)

    I went from Jersey to Pennsylvania, mostly using County Roads in Jersey on the way out, and there were a few 25 mph zones and some red lights along the way. On the way back, I used Interstate 78 and 287 for the most part. (Our northeastern readers will know exactly what roads those are.) I had the windows open for the entire duration, and I did a decently high speed on the way back, enough to be detrimental to gas mileage (as far as I know.)

    So, I actually managed to do 18.725 miles per gallon when I finally went and refilled the tank. (The whole trip wasn't 131.15 miles, but that was the mileage in between the last fill up to that fill up. I did that for accuracy.)

    This I think is actually pretty good, given that my Fifth Avenue still has crooked steering (alignment out) and runs a bit rich. (It's a stock car. Still has lean burn and all.)

    Out of curiosity, is there anyone else here that would like to share their gas mileage rates? I'd like to see how they compare. (I know, who owns a fifth avenue for the gas mileage, right?)
     
  2. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,152
    Likes Received:
    259
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    My Dad said his 84 did 25Canadian on the hiway,on a regular basis.That would be 20USg. But my Daddy was not easy on the pedals.
     
  3. Aspen500

    Aspen500 Well-Known Member

    Messages:
    5,002
    Likes Received:
    1491
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    My Aspen averages about 9-10 mpg but waaaaaaay back when it was still a 225/4-speed it got 16-18 mpg avg. Best ever was 22 on a highway trip. Keep in mind, at that time, the national speed limit was still only 55 mph though and at that speed with an E24 225 (90 hp), O/D was useless on anything but level road and around here that's not too common (seems like you're always going uphill or downhill).
     
  4. Mr C

    Mr C Well-Known Member

    Messages:
    299
    Likes Received:
    82
    Joined:
    Apr 22, 2014
    Pretty good...I'm averaging @ 15 MPG combined on the 5th Ave that is my daily.
     
  5. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,152
    Likes Received:
    259
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    For a daily the hiway mileage number often drops to 70% or even 60% and in winter 50%. So then 15 doesn't sound so bad.
    My fancy DI 2.4 VVT Orlando/Ecotec falls to 27 typical, from 40 hiway, which being 67.5%.. It is what it is.
     
  6. toolmanmike

    toolmanmike Super Moderator Staff Member

    Messages:
    53
    Likes Received:
    13
    Joined:
    Feb 27, 2011
    18-20 is a pretty good average. I get 19 and change with my HP 273 in my 66 and about the same with my 318 Swinger. Both have 3.23's and got that mileage with 14" or tall 15's. If I would poke along at 50 mph for hours at a time on the interstate I could probably get 20+.
     
  7. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,152
    Likes Received:
    259
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    I have ,over the years, stumbled on data to the effect that if you reduce your cruise rpm x percent, your fuel-economy can be expected to rise by about half of that per cent.
    So from 65 to 50 is a decrease of about 23%
    therefore, by that yardstick, you might expect an 11.5% increase in economy, or from 18 to 20mpg.

    I once decreased my cruise rpm from 2600@56mph to 1800@75 and my economy jumped from low 20s to low 30s. It would be hard to make an apples to apples comparison with those differing baselines, but it is, in any case, remarkable the effect rpm and speed have on fuel useage.
     
    toolmanmike likes this.
  8. MoparDan

    MoparDan Well-Known Member

    Messages:
    275
    Likes Received:
    28
    Joined:
    Mar 17, 2011
    Location:
    Daytona Beach, FL
    Currently 13-15 mpg pretty much all stop and go traffic. A long time ago when the alignment was better and the engine didn't stall I once did as good as 35 or 36 mpg (figured out with a mpg calculator) on a trip from CT to North Carolina, going about 65 the whole way, stock 318 with computer
     
  9. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,152
    Likes Received:
    259
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    Remarkable!
    When you say it had a computer, do you mean it was an EFI'd Magnum?
    Or a LeanBurn,
    Or a custom set-up.
     
  10. MoparDan

    MoparDan Well-Known Member

    Messages:
    275
    Likes Received:
    28
    Joined:
    Mar 17, 2011
    Location:
    Daytona Beach, FL
    Lean Burn with factory carb. sorry I wasn't clearer
     
  11. Master M

    Master M Well-Known Member

    Messages:
    306
    Likes Received:
    109
    Joined:
    Nov 22, 2014
    On the interstate and some town driving getting there with a/c on, and the interstate speed of 75 mph, the 1988 5th. in original condition got 20 mpg going and return trip got 21 mpg.
     
  12. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    1,152
    Likes Received:
    259
    Joined:
    Apr 26, 2016
    Location:
    On the Circle of the earth, Southern Man,Canada
    Wow; even more impressive.
     
    MoparDan and toolmanmike like this.
  13. IndieDippy

    IndieDippy Well-Known Member

    Messages:
    161
    Likes Received:
    36
    Joined:
    Jul 22, 2017
    Location:
    Baltimore
    my mileage is garbage. sometimes i feel like my gas is disappearing into thin air. park it at a quarter tank get back in its at half. haven't quite figured out the exact rate but i reckon around 12 to 15 mpg. pleeeeease tell me how i can get 30 mpg in a Diplomat. most of my driving is on country roads and city/suburban streets