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Thread: Gas mileage suggestions

  1. #1
    Join Date
    Apr 2009
    Location
    Houston
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    95

    Default Gas mileage suggestions

    Let me start by saying I realize I am driving a 79' carbed 345 v8 with heavy axles and drive line. That being said it took 40 bucks to drive 75 miles this weekend. Does any one have any suggestion to improve the mileage? Filters and pump are new. Does the pertronix device deliver in this area?

  2. #2
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

    Default

    That's about half the gas mileage you should be getting. There's something wrong. I get better economy with my fire truck w/304, and it weighs as much as 3 scouts. I get better economy in my school bus with 345 and it weighs as much as 4 scouts.

    Check the mixture. No amount of spark degradation would cause this unless half your plugs are dead. You must be running incredibly rich. Whatever is causing this, it's got to be pretty basic.

    What rpm do you run on the highway at 65 mph?
    Do you have a manual or automatic? If auto, the slippage would be obvious if your engine is running well.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

  3. #3
    Join Date
    Apr 2009
    Location
    Houston
    Posts
    95

    Default gas

    I have no tach I can't tell you the RPM at highway speed. I was running close to 70 which is a little higher than usual. I also noticed the breather tube under the tank filler pipe is loose so it could have evaporation issues. It has the Rochester Quadrajet which i have never adjusted because I don't know how. It is an automatic and it sits on 31" tires. Timing could be off also. I have never felt like it had enough power compared to the size of the displacement. I started the points at .016 and ended up at .021 and got a dwell at 25.

  4. #4
    Join Date
    Feb 2009
    Location
    Paso Robles, Ca
    Posts
    63

    Default

    Quote Originally Posted by jtl1100 View Post
    Let me start by saying I realize I am driving a 79' carbed 345 v8 with heavy axles and drive line. That being said it took 40 bucks to drive 75 miles this weekend. Does any one have any suggestion to improve the mileage? Filters and pump are new. Does the pertronix device deliver in this area?
    How does your engine sound while driving? Is it backfiring or missing? what do your plugs look like?
    For Carb adjustment, goto Holley.com and watch the videos on carb adjustment. Try to keep your speed down a little and that should help, your not going to get the 5-6 MPG's back just by slowing down, but will help a little.
    You should be able to get close to 10 MPG by just some minor tuning.

  5. #5
    Join Date
    Jun 2009
    Location
    Hurlburt Field, FL
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    495

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    I know it might be a long shot, but I've seen IH v-8's run "fine" before and only on 7 or even 6 cylinders. Maybe pull your valve covers off and check to make sure all the lifters are working? If even one isn't working, your engine would be working double overtime to keep the rpm's up when you're on the highway.

  6. #6
    Join Date
    Apr 2009
    Location
    Houston
    Posts
    95

    Default

    IT seems to be running smoothly, no noticable hopping or anything. Not backfiring eather. Unfortunately I have 60 hours of Microbiology and work to do before I have a chance to tear in to it again. Since the breather tube came off I am really hoping to find I lost excessive gas due to evaporation. However, I will definately check out the Holley site. If I was running incredibly rich would I see black smoke? I don't it actually sounds like it is running really well. I should also mention the day it burned so much gas it was over 100 degrees. Will pull the plugs this week end. Thanks for the help and all suggestions are welcome.

  7. #7
    Join Date
    Apr 2009
    Location
    Houston
    Posts
    95

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    Ok. So the hose that is my breather tube came loose. It is heater hose. Will that be ok? I noticed it shrank and came loose fromt the top part not the tank part. I replaced with a little longer heater hose and hope its long enough to account for the shrinkage in the heat. Hah hah snicker snicker.

  8. #8
    Join Date
    Apr 2009
    Location
    Houston
    Posts
    95

    Default

    Just a follow up. I replaced the breather tube and my mileage is acceptable again.

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