78GT Aerodynamics !! or lack of...

Discussion in 'General Ranchero Help' started by lovejoy, Jun 24, 2021.

  1. lovejoy

    lovejoy In Second Gear

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    55
    Hi guys, any opinions about improving the gas mileage by adding a bed cover to reduce turbulence, I keep a large mat in the rear bed area, up behind the cab, and notice it gets blown about at speeds over 40mph.
    I am getting about 16 mpg ( UK galleons, 4.55 liters) with the 400 / C6 combination,
    so any improvement will be good.
    How to attach the cover will present some thought, especially below the rear window area, as that will be lower than the sides?
    Any suggestions welcome, I see some nice covers on google images of 72 to 79 Rancheros.
    Cheers guys.
     
  2. Clark

    Clark In Maximum Overdrive

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    16 mpg! Wow! My '75 460 gets 9 mpg in town and a whopping 15 mpg on the highway. Of course, gasoline was about 50 cents a gallon when I bought that new '75 GT.

    I don't think aerodynamics is the issue with a 2 ton truck.
     
    The Wrench likes this.
  3. 1978GT

    1978GT In Fourth Gear GOLD MEMBER

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    338
    I think he has calculated his mileage in Imperial (UK) gallons, which are approximately 20% larger than US gallons. The 16 would then equate to about 13.3 MPG in US measure.

    I always say my 78 gets 20 MPG - 9 city and 11 highway!

    There are many factors in gas mileage, including the driver's right foot (mine is very heavy).
     
    ForistellFord likes this.
  4. uk ranchero

    uk ranchero In Second Gear

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    91
    mine had a bed cover when i first got it. fixed to back of the cab with a ally channel with a wire sewn into the front end of the cover. don't use it now. swapping the transmission for something with a overdrive top might help*. best thing is never work out your gas mileage you know it ain't good you know UK gas prices.


    * unlikely as cruising at higher speeds is more fun.
     
  5. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    My '79 GT averaged 16 MPG highway with a canopy and 600 pounds weight in the back, but I have very short ratio rear gears, 2:47 to 1.
     
  6. lovejoy

    lovejoy In Second Gear

    Messages:
    55
    Aha, I forgot to mention the rear axle ratio, it is "2"
    on the drivers door pillar i.d. info, which indicates a very tall
    2.75 , and having rebuilt the 2bbl Autolite carburetor,
    I know the main jets are both #50, so much leaner than the#57 they should be.
    At "UK Ranchero", where are you situated, anywhere near the south coast, by any chance??
    The idea of the bed cover is two-fold, one to keep out water when carrying items that need to keep dry,
    two, to even the airflow across the rear, I usually cruise at 65 mph going west down Interstate A30, for 200 miles,
    the tacho indicates 2,350 rpm, and I use up 12 of our overpriced British Galleons, generally Tescos cheapest unleaded.
    I don't expect miracles from such a heavy truck, but am very aware that the airflow from over the cab slams into the inner tailgate panel, hence the turbulence !!
    Thanks for the replies so far, I don't think I will be having an overdrive gearbox replacement fitted in place of the bulletproof power consuming C6
     
  7. beerbelly

    beerbelly In Maximum Overdrive SILVER MEMBER

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    You might find this interesting:
     
  8. Hillbilly

    Hillbilly In Maximum Overdrive

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    For what it is worth, my 2004 F-350 four door long bed truck get's two miles per (US) gallon more with the toneau cover closed than it does with the bed open.
     
  9. lovejoy

    lovejoy In Second Gear

    Messages:
    55
    Beerbelly, thanks for that !
    I think that says it all, confirms my belief !!
    Now to find a suitable tonneau cover, or get one made ...
    Maybe "UK Ranchero" will sell me his, if he doesn't want it ?
    I will try a private message,
    keep on trucking
     
  10. Hillbilly

    Hillbilly In Maximum Overdrive

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    Very interesting video, thanks! That explains the wide tops on modern tailgates, and I thought it was for extra support for the aluminum gates. Without a smoke generator and wind tunnel all I could relate to is the feel of my truck comparing the open bed to when the tonneau cover was closed. Got the old style thin top tail gate and the buffeting was really noticeable with the bed open. Covered bed also seems to stop the buffeting when towing an enclosed car trailer.
    Dad has a huge wing type spoiler on the roof of his F-450 that deflects the wind nicely even when towing a two car stacker trailer. His truck feels good even with no bed cover.
     
  11. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    Location:
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    My mom bought a 1980 Silverado for her and Dad's Silver Anniversary, and I remember it saying on the window sticker, something like 12 or 14 MPG back then, but when she put a basic canopy on it, she immediately gained 2 mpg (according to Dad), and that was with a 305-2V and TH-200 (a crappy slushbox).
     
  12. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    12,133
    Location:
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    With Babe's canopy, and the 2.47 gears, I averaged 16 MPG on my way down here a year ago January.
     
  13. uk ranchero

    uk ranchero In Second Gear

    Messages:
    91
    as it happens yes not far from portsmouth

    my cover , if i still have it is not useable as it has shrunk
     

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